Definify.com
Webster 1913 Edition
Q
Q
(kū)
, the seventeenth letter of the English alphabet, has but one sound (that of k), and is always followed by u, the two letters together being sounded like kw, except in some words in which the u is silent. See Guide to Pronunciation, § 249. Q is not found in Anglo-Saxon, cw being used instead of qu; as in cwic, quick; cwen, queen. The name (kū) is from the French ku, which is from the Latin name of the same letter; its form is from the Latin, which derived it, through a Greek alphabet, from the Phœnician, the ultimate origin being Egyptian.
Etymologically, q or qu is most nearly related to a (ch, tch), p, q, and wh; as in cud, quid, L. equus, ecus, horse, Gr. [GREEK], whence E. equine, hippic; L. quod which, E. what; L. aquila, E. eaqle; E. kitchen, OE. kichene, AS. cycene, L. coqu ina.Webster 1828 Edition
Q
Q
is the seventeenth letter of the English Alphabet; an articulation borrowed from the oriental koph or qoph, Hebrew. It is supposed to be an articulation more deeply guttural than that of K; indeed it might have been pronounced as we pronounce qu; for we observe that in the Latin language, from which the moderns have borrowed the letter, it is always followed by u, as it is in English. This letter is not in the Greek alphabet. This letter is superfluous; for ku or koo, in English, have precisely the same sounds as qu. It is alleged that in expressing q, the cheeks are contracted, and the lips put into a canular form, for the passage of the breath; circumstances which distinguish it from k. This appears to be a mistake. This position of the organs is entirely owing to the following letter u; and kuestion and question are pronounced precisely alike, and with the same configuration of the organs. It appears then that q is precisely k, with this difference in use, that q is always followed by u in English, and k is not. Q never ends an English word.As a numeral, Q stands for 500, and with a dash above the Q, for 500,000.
Used as an abbreviation, Q stands for quantity, or quantum; as among physicians, q. pl. quantum placet, as much as you please; q s quantum sufficit, as much as is required, or as is sufficient.
Among mathematicians, Q.E.D. stands for quod erat demonstrandum, which was to be demonstrated; Q.E.F. quod erat faciendum, which was to be done.
In English, Q is an abbreviation for question.