The Collaborative International Dictionary of English v.0.48:

A \A\ (named [=a] in the English, and most commonly [aum] in
   other languages).
   The first letter of the English and of many other alphabets.
   The capital A of the alphabets of Middle and Western Europe,
   as also the small letter (a), besides the forms in Italic,
   black letter, etc., are all descended from the old Latin A,
   which was borrowed from the Greek Alpha, of the same form;
   and this was made from the first letter (?) of the
   Ph[oe]nician alphabet, the equivalent of the Hebrew Aleph,
   and itself from the Egyptian origin. The Aleph was a
   consonant letter, with a guttural breath sound that was not
   an element of Greek articulation; and the Greeks took it to
   represent their vowel Alpha with the [aum] sound, the
   Ph[oe]nician alphabet having no vowel symbols.
   [1913 Webster] This letter, in English, is used for several
   different vowel sounds. See Guide to pronunciation,
   [sect][sect] 43-74. The regular long a, as in fate, etc., is
   a comparatively modern sound, and has taken the place of
   what, till about the early part of the 17th century, was a
   sound of the quality of [aum] (as in far).
   [1913 Webster]

   2. (Mus.) The name of the sixth tone in the model major scale
      (that in C), or the first tone of the minor scale, which
      is named after it the scale in A minor. The second string
      of the violin is tuned to the A in the treble staff. -- A
      sharp (A[sharp]) is the name of a musical tone
      intermediate between A and B. -- A flat (A[flat]) is the
      name of a tone intermediate between A and G.
      [1913 Webster]

   A per se (L. per se by itself), one pre["e]minent; a
      nonesuch. [Obs.]
      [1913 Webster]

            O fair Creseide, the flower and A per se
            Of Troy and Greece.                   --Chaucer.
      [1913 Webster]