Ø

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A letter O with a stroke. Used as vowel in some Scandinavian alphabets.
• noun mathematics A symbol for the empty or null set: the set with no elements.
• noun linguistics A symbol for a null form commonly used instead of ∅: one that is never expressed in speech or writing, but that appears to play a grammatical role; for example, English may be said to have a usual plural suffix -s and a zero plural suffix -Ø for some nouns such as sheep and Portuguese.