An alpha privative or, rarely,[1] privative a (from Latin alpha prīvātīvum, from Ancient Greek α στερητικόν) is the prefix a- or an- (before vowels) that is used in Indo-European languages such as Sanskrit and Greek and in words borrowed therefrom to express negation or absence, for example the English words of Greek origin atypical, anesthetic, and analgesic.
It is derived from a Proto-Indo-European syllabic nasal *n̥-, the zero ablaut grade of the negation *ne, i.e. /n/ used as a vowel.
In Latin, the cognate prefix is in-, which leaves its traces in English words like invisible and inaccessible.
In North Germanic languages, the -n- has disappeared and Old Norse has ú- (e.g. ú-dáins-akr), Danish and Norwegian have u-, whereas Swedish uses o- (pronounced [u]), and Icelandic and Faroese use the related ó-.
The prefix ἁ- ha- (also ἀ- a- from psilosis), copulative a, is nearly homonymous with privative a, but originates from Proto-Indo-European *sm̥.