The vowel [a] is most common vowel in Adûnaic, and could be both short and long (SD/422-3). The long [a] could arise through primitive vowel-lengthening or a-fortification, or from the contact of two instances of [a] due to the loss of an intervening consonant. The process of a-infixion served an important role in the Adûnaic subjective case, and [a] is a common element in the last syllable of neuter-nouns.

Towards the end of the Classical Adûnaic period, a short final [a] was often omitted in speech before another vowel or at the end of a phrase, but this did not apply to written Adûnaic (SD/434).