The horn (
Vietnamese: dấu móc or dấu râu) 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, they are rarely considered as diacritics; but rather, the characters ơ and ư are considered as different letters from o and u.