What does an O with a slash through it mean?

What does an O with a slash through it mean?

Ø, ø is a distinct letter in the Norwegian, Danish, and Faerose alphabets. The slash across the o originally indicated an additional e, compared to the ligature œ seen in French. This letter is separate and not interchangeable with the letter o.

It could denote a diameter measurement. Ø = 15 mm means some pipe or shaft diameter is 15 mm. Ø denotes the empty or null set.

Similar to the empty set, as a slashed zero, it might help distinguish between the unslashed zero 0 and the capital O.

The ø also can be found as a written variant of the Greek letter ϕ, Phi, though the standard version of that letter has a vertical bar. Note that the Theta, θ, has a horizontal bar, but its bar stays inside the ellipse. As the Greek letter, it might be used to indicate a function, phase, or angle.

What does an O with a slash through it mean?

Normally, an O with a slash through it, i.e., Ø, stands for the Greek letter Phi. It is also used to denote the diameter of a pipe. For example, in the context of a pipe, outer Ø = 10 cm would mean a pipe of external diameter 10cm.

And here is another perspective on this question:

It depends on the context. In certain Scandinavian languages, it’s an alphabetic character.

In mathematics, it represents a ‘null set’.

In common usage, it’s come to represent either a prohibition on something or, in some fonts, simply the digit ‘zero.’

I’m a big advocate of using slashed zeros, as it’s the only effective way to distinguish it from the letter “O.” As someone who has to do a lot of math and has terrible handwriting, this is a big deal. I also put slashes in my 7’s and Z’s for the same reason.

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Is a slash used on a zero or an O to differentiate between the two?

For distinguishing the digit 00 from the letter O, you always put the slash through the digit rather than the letter, but…

Other symbols may also confuse, including:

  • ∅∅ or ∅∅ for the empty set, which I prefer to write as {}{}
  • ϕ,φ,θ,ϑ�,�,�,� for lowercase Greek letters
  • Φ, ΘΦ, Θ for upper case Greek letters
  • ø or Ø for Scandinavian letters
  • ⊘,⊖,⊝⊘,⊖,⊝ and other mathematical symbols

The context is usually decisive, but to completely avoid ambiguity, you might have to use a word or phrase rather than just a symbol.

How do I tell between the letter o and the number 0?

The letter o (O) typed is rounder and more circular. The digit 0 is more of an egg shape. Narrower and thinner. So, For each one below, is it the digit Or the letter?

  1. O
  2. 0
  3. o
  4. 0

What symbol has a zero and a straight line inside it?

LATEX����� has quite a few symbols that might match your description, including:

  • \Theta ΘΘ
  • \theta θ�
  • \emptyset ∅∅
  • \varnothing ∅∅
  • \circleddash ⊝⊝
  • \ominus ⊖⊖
  • \oslash ⊘⊘
  • \Phi ΦΦ
  • \phi ϕ

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What is the name of the “o” with a vertical slash across it used in Scandinavian alphabets?

In the Scandinavian languages that use the letter ø, called similarly to other vowels: by using the vowel sound itself. Just like <e> is called [e:], ø is called [ø:]. It is, therefore, the same as ö.

The same symbol is used in IPA to represent the rounded mid-close vowel, and the name of this IPA symbol is “Latin small letter o with stroke.”

Why do Europeans put a slash in the number 7?

This is a continental European thing. The British normally don’t. It’s to prevent confusion with 1. Continental Europeans often write 1 with a very long initial stroke, as it is written here:

So, a seven is written with an extra stroke to ensure no confusion.

What does “slash” mean in British slang?

When I was a kid, it was a slang term for urinating. The English language has a remarkable lexicon regarding various bodily functions.

As men, take a “whiz,”… “drain the snake,”… go for a “piddle,”… and, of course, take a piss. Ladies are much more sophisticated.

What does θ� mean in mathematics? Where does it come from?

Most often, θ is a variable that stands for an angle in geometry, e.g.:

There’s nothing special about it; it’s just a convention that lower-case Greek letters represent angles. The convention goes back to Euclid.

θ is often used with φ to represent angles in two different planes in three-dimensional geometry. Generally, φ represents longitude, and θ represents latitude, though the choice is arbitrary. Two angles in the same plane are often represented by α and β.

Theta has many other uses. In computer science, it represents a function that restricts a join (corresponding roughly to the WHERE clause in SQL), and the upper-case Θ is used in algorithm analysis. It’s also used in meteorology, particle physics, and economics.

But if you’re seeing it in math, it almost certainly represents a plane angle unless you’re told otherwise.

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How do I pronounce ‘O’ with a slash?

I assume it’s in Norwegian or Danish; if it’s in another language, especially a non-Northern European language, then this answer is probably not helpful.

It’s similar to an ö: round your lips as tightly as is comfortable, but with a small opening for the sound to come out, and try to say “er,” but without the ‘r’ sound. That’ll give you the approximate sound.

Why does a zero have a line through it?

Both zero and the capital letter O look similar, so in some contexts, we specialize one of them to distinguish them more easily. We might add a dot or slash, make them different sizes, or give them noticeably different shapes.

Compare and contrast how the font selections here distinguish the two:

Quora’s normal text font: 0 O

Quora’s inline code font: 0 O


Roman: 0 O


Teletype: 0 O

The current convention typically specializes in the zero if we add a slash or a dot. But that wasn’t always the case, as you can see in this old TI-990/12 minicomputer schematic.

And elsewhere in the same schematic:

That looks weird to my eyes.

Why is there a line through the O in Brønsted?

It’s not an O with a line through it. It’s an ø. That’s like asking why it is an L with a line through it. Visually, sure, that’s how the letter was designed. But it’s a completely different letter (and sound) in Norwegian, Danish, and Faroese. (Swedish and Icelandic spell it ö. That spelling is also used in German and some other languages.)

The pronunciation is halfway between /o/ and /e/, at least as pronounced in those languages. Halfway between the pronounced names of the letters O and A, in English, ‘spelling.’ (English spelling makes all of this confusing!) 

Technically, it’s a front rounded vowel, which means that your tongue is in the front of your mouth like to say /e/, but then your lips are rounded like saying /o/. (Note that /e/ is a front unrounded vowel, and /o/ is a back rounded vowel.) It is hard to explain this in text if you’re not used to it since we don’t have the sound in English.

In other words, to pronounce the first syllable of brønsted, you could try saying brain but then making your lips round like you’re saying “no” or “oh,” but without moving your tongue. 

Actually, since in Norwegian, the letter can sometimes be a reduced vowel sound (like our ‘schwa,’ as in “about”), you can try saying that a little reduced too, maybe sort of like ‘brin’ or ‘bren’ with lip rounding. 

I hesitate to post this silly music video because it might get stuck in your head, but you won’t forget the Norwegian alphabet after this!

What does an O with a vertical line through it mean?

It may be the Cyrillic letter “ef,” but more likely the Greek letter “phi,” which has several scientific or technical meanings, although the most common one is the mathematical concept “null set.” Giving the vertical line a slight rightward tilt is more common.

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What does the Phi symbol mean in math?

The Greek letter Phi, written ΦΦ or ϕ� or�, is used as a variable in many ways. For example, it and other Greek letters are commonly used for angles.

Sometimes ϕ� denotes the empty set, but other symbols, including and, are usually used for that ∅. (The empty set is the set that has no elements.)

Why is the number zero (0) read as the alphabet letter “O” by most U.S. people?

Zero is slightly longer to pronounce, hence the “oh.” As an American speaker, I’ve always heard it pronounced one ‘oh’ one, though that doesn’t make it any more correct than one zero one or one-hundred and one even.

It also tends to be a little more trendy and less formal to use ‘oh’ (Hawaii Five-Oh, for example).

The Oxford English Dictionary says:

O n. (also oh) zero (in a sequence of numerals, especially when spoken).

American speakers use zero in both conversation and writing. When reciting a string of numbers only, it is acceptable and common for an American to pronounce zero as “oh.” But when reciting a string that mixes characters and numbers, it becomes necessary to differentiate between “oh” and zero.

In British English, zero is normally used only in scientific writing. In conversation, British speakers usually say “naught” or, to a lesser degree, “oh.”

Is vocalizing “slash” acceptable in English?

It is just fine. Nobody owns English. Or does everybody own English? English is a messy, evolving language, and people who try to control it often look silly.

Much of English’s flexibility and complex, awkward beauty comes from its messiness.

English has many words from other languages. It has many conflicting grammatical rules. Today’s English is quite different from the English of 200 years ago. And the online communication evolution of the language will likely likely speed up. This may be uncomfortable, and many people, myself included, might not enjoy the new variants—LEET-speak ick.

Certainly, newspapers and content creators can set their own rules and do so with their official Style Guides.

And you can set your own rules for your English.

Don’t try to set mine. That would be “unacceptable” to me, though I might listen if you seem smart.


Anywhere that the distinction between the digit “zero” (“0”) and the Latin script letter “O” needs to be highlighted, such as in encoding systems, scientific and engineering applications, computer programming (such as software development), and telecommunications, the slashed zero glyphs is frequently used.

In the languages of Danish, Norwegian, Faroese, and Southern Sámi, the letter is known as (or minuscule: ). Except for Southern Sámi, where it is employed as a [oe] diphthong, it is mostly used to express mid-front rounded vowels like [] and [oe] (listen).


The slashed zero glyphs are often used to distinguish the digit “zero” (“0”) from the Latin script letter “O” anywhere that the distinction needs emphasis, particularly in encoding systems, scientific and engineering applications, computer programming (such as software development), and telecommunications.

What does an O with a slash through it mean?

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