The horn is a diacritic mark attached to the top right corner of the letters o and u in the Vietnamese alphabet to give ơ and ư, unrounded variants of the vowel represented by the basic letter. In Vietnamese, it is rarely considered a separate diacritic; rather, the characters ơ and ư are considered separate from o and u.

The HTML codes for letters with a horn are:

Horn (diakritisches Zeichen)

Diacritics | Vietnamese language