A a Roman Character, A a Italick, A a old English, A α Greek, א Hebrew, are the first Letters of the Alphabet; and in all Languages, ancient and modern, the Character appropriated to the same Sound is the first Letter, except in the Abissine.
A Foreigner finds it very difficult to learn how to pronounce our a, in different Words; it having four distinctly differing Sounds; two long, as in Wake, Wall; and two short, as in Wax, Was, and hardly any Rules how to distinguish them, but what are liable to a greater Number of Exceptions.
The Dipthongs form’d with it are liable to as great Difficulties.

Definition taken from The Universal Etymological English Dictionary, edited by Nathan Bailey (1736)

[previous] * A [among the Ancients]
A [among the Ancients]
Ā, or ā
A [among the Romans]
Absoˊrb [with Gardeners, &c.]
Action [in Physics]