Old English cwic "living, alive, animate," and figuratively, of mental qualities, "rapid, ready," from Proto-Germanic *kwikwaz (source also of Old Saxon and Old Frisian quik, Old Norse kvikr "living, alive," Dutch kwik "lively, bright, sprightly," Old High German quec "lively," German keck "bold"), from PIE root *gwei- "to live." Sense of "lively, swift" developed by late 12c., on notion of "full of life."
NE swift or the now more common fast may apply to rapid motion of any duration, while in quick (in accordance with its original sense of 'live, lively') there is a notion of 'sudden' or 'soon over.' We speak of a fast horse or runner in a race, a quick starter but not a quick horse. A somewhat similar feeling may distinguish NHG schnell and rasch or it may be more a matter of local preference. [Carl Darling Buck, "A Dictionary of Selected Synonyms in the Principal Indo-European Languages," 1949]Of persons, "mentally active," from late 15c. Also in Middle English used of soft soils, gravel pits, etc. where the ground is shifting and yielding (mid-14c., compare quicksand). As an adverb from c. 1300. To be quick about something is from 1937. Quick buck is from 1946, American English. Quick-change artist (1886) originally was an actor expert in playing different roles in the same performance of a show. Quick-witted is from 1520s.
"living persons," Old English cwic, from quick (adj.); frequently paired with the dead, as in Old English cwicum & deadum. The quick "tender part of the flesh" (under a nail, etc.) is from 1520s, as is the figurative use of it.