D defs.my
Entry 3 senses Webster, 1913

D

/(dē)/ · IPA /diː/
01 The fourth letter of the English alphabet, and a vocal consonant. The English letter is from Latin, which is from Greek, which took it from…
  1. 1.
    The fourth letter of the English alphabet, and a vocal consonant. The English letter is from Latin, which is from Greek, which took it from Phœnician, the probable ultimate origin being Egyptian. It is related most nearly to t and th; as, Eng. deep, G. tief; Eng. daughter, G. tochter, Gr. qyga`thr, Skr. duhitr. See Guide to Pronunciation, √178, 179, 229.
  2. 2.
    The nominal of the second tone in the model major scale (that in C), or of the fourth tone in the relative minor scale of C (that in A minor), or of the key tone in the relative minor of F.(Mus.)
  3. 3.
    As a numeral D stands for 500. in this use it is not the initial of any word, or even strictly a letter, but one half of the sign � (or � ) the original Tuscan numeral for 1000.