'Quick' meant 'alive,' not 'fast' — from PIE *gwih3wos, kin to Latin 'vivus.' Speed came from liveliness.
Moving fast or doing something in a short time; prompt to understand or respond.
From Old English "cwic" ("alive, living, animate"), from Proto-Germanic *kwikwaz ("alive"), from PIE *gʷih₃wós ("alive, living"), a reduplicated or suffixed form of *gʷeyh₃- ("to live"). This PIE root is one of the most important in the Indo-European vocabulary of life: it produced Latin "vīvus" ("alive," yielding "vivid," "vivacious," "revive," "survive"), Greek "βίος" (bíos, "life," yielding "biology," "biography"), Sanskrit "jīvá-" ("living"), Old Irish "beo" ("alive"), Lithuanian "gývas" ("alive"), and Old Church Slavonic "živŭ" ("alive"). The Old English meaning was emphatically "alive" — the phrase "the quick and the dead" (preserved in the Apostles' Creed) meant "the living and the dead," not "the
The phrase 'the quick and the dead' in the Apostles' Creed does not mean 'the fast and the dead' — it means 'the living and the dead,' preserving the word's original Old English meaning. 'Quicksilver' (mercury) was named because the liquid metal seemed alive as it moved, and 'quicksand' was sand that appeared to be living because it shifted and swallowed things.