slashed-O (Ø, ø): zero, nothing. (Typographically, a letter O with a slash [3]. The upper-case (Ø) and lower-case (ø) forms are often used interchangeably, whichever looks best in a particular context. The symbol presumably originated as a typographical substitute for the null sign of symbolic logic (), and sometimes that symbol is still used instead of the slashed-O.) The symbol has several distinct uses in linguistics.

slashed-O (Ø) [1]: a symbol which is used in descriptions of linguistic changes, especially phonological ones, to indicate a deletion or an epenthesis (insertion). For example, iflechaØ means that i is deleted, and Øflechai means that i is inserted. [Spanish: O con diagonal [1]]

slashed-O (Ø, ø) [2]: a symbol which is used, when dividing a word into morphemes, to indicate a zero morpheme. For example, in Nahuatl the verb "nemiskeh" 'they will walk' can be divided "ø-nemi-s-keh" (they-walk-future-plural). [Spanish: O con diagonal [2]]