Thealpha privativum, used to make words that have a senseopposite to the word (orstem) to which theprefix is attached. It is also known asprivative a andalpha privative; a-, ab-, an-, anti-, contra-, de-, dis-, ex-, il-, im-, in-, ob-, ne-, non-, not, un-
The alpha is usually short, but long when added to a stem that begins with three short syllables. Thus, words such asἀ-δάματος(a-dámatos) begin with long alpha inEpic, and frequently also in Lyric, Tragic, or Comic poetry.ἀθάνατος(athánatos) and all its compounds always have long alpha.
