quick [OE] The original meaning of quick in Old English was ‘living’ or ‘alive’, contrasting with something dead or inanimate. This early sense still survives in the expression the quick and the dead, meaning ‘the living and the dead’, which comes from the Apostles’ Creed in the Book of Common Prayer (1662): ‘From thence he shall come to judge the quick and the dead.’ Quicksand [OE] is so called because it moves—and swallows things up—as if it were alive. The original ‘alive’ sense of quick also led to the use of the word to refer to the soft, tender flesh below the growing part of a fingernail or hoof [LME]. This area is well supplied with nerves and is very sensitive to touch or injury (and so seems more ‘alive’ than other parts of the skin). So to cut someone to the quick [M20th] is to upset them very much by saying or doing something hurtful. It was a simple step in the word’s history to go from ‘alive’ to senses such as ‘lively’ and ‘vigorous’ and, from the late 16th century, ‘fast’. mercury was formerly known as quicksilver—the silver substance moves in such an unpredictable way that it seems to be alive.