QyoudaoicibaDictYouDict[Q 词源字典]
16th letter of the classical Roman alphabet, from the Phoenician equivalent of Hebrew koph, qoph, which was used for the more guttural of the two "k" sounds in Semitic.

The letter existed in Greek, but was little used and not alphabetized; the stereotypical connection with -u- began in Latin. Anglo-Saxon scribes adopted the habit at first, but later used spellings with cw- or cu-. The qu- pattern returned to English with the Norman Conquest and had displaced cw- by c. 1300. In some spelling variants of late Middle English, quh- also took work from wh-, especially in Scottish and northern dialects, for example Gavin Douglas, Provost of St. Giles, in his vernacular "Aeneid" of 1513:
Lyk as the rois in June with hir sueit smell
The marygulde or dasy doith excell.
Quhy suld I than, with dull forhede and vane,
With ruide engine and barrand emptive brane,
With bad harsk speche and lewit barbour tong,
Presume to write quhar thi sueit bell is rong,
Or contirfait sa precious wourdis deir?
Scholars use -q- alone to transliterate Semitic koph (as in Quran, Qatar, Iraq ). In Christian theology, Q has been used since 1901 to signify the hypothetical source of passages shared by Matthew and Luke, but not in Mark; in this sense probably it is an abbreviation of German Quelle "source."[Q etymology, Q origin, 英语词源]