clock (n.1) Look up clock at Dictionary.com
late 14c., clokke, originally "clock with bells," probably from Middle Dutch clocke (Dutch klok) "a clock," from Old North French cloque (Old French cloke, Modern French cloche), from Medieval Latin (7c.) clocca "bell," probably from Celtic (compare Old Irish clocc, Welsh cloch, Manx clagg "a bell") and spread by Irish missionaries (unless the Celtic words are from Latin); ultimately of imitative origin.

Replaced Old English dægmæl, from dæg "day" + mæl "measure, mark" (see meal (n.1)). The Latin word was horologium; the Greeks used a water-clock (klepsydra, literally "water thief"). Image of put (or set) the clock back "return to an earlier state or system" is from 1862. Round-the-clock (adj.) is from 1943, originally in reference to bomber air raids.
clock (v.) Look up clock at Dictionary.com
"to time by the clock," 1883, from clock (n.1). The slang sense of "hit, sock" is 1941, originally Australian, probably from earlier slang clock (n.) "face" (1923). Related: Clocked; clocking.
clock (n.2) Look up clock at Dictionary.com
"ornament pattern on a stocking," 1520s, probably identical with clock (n.1) in its older sense and meaning "bell-shaped ornament."