a

a is a Noun

Definition:

[1] 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 (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 ä sound, the Phoenician alphabet having no vowel symbols. This letter, in English, is used for several different vowel sounds. See Guide to pronunciation, §§ 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 ä (as in far).

[2] 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#) is the name of a musical tone intermediate between A and B. -- A flat (A) is the name of a tone intermediate between A and G.