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The prefix a- or an- before vowels, used in Greek and in English words borrowed from Greek to express absence or negation.
(Linguistics) (in Greek grammar) the letter alpha (or an- before vowels) used as a negative or privative prefix. It appears in English words derived from Greek, as in atheist, anaesthetic
the prefix a- or, before a vowel, an-, used in Greek and English to express negation or absence.