Clock1  —n. 1 instrument for measuring and showing time. 2 a measuring device resembling this. B colloq. Speedometer, taximeter, or stopwatch. 3 slang person's face. 4 seed-head of the dandelion. —v. 1 colloq. A (often foll. By up) attain or register (a stated time, distance, or speed). B time (a race) with a stopwatch. 2 slang hit.  clock in (or on) register one's arrival at work. Clock off (or out) register one's departure from work. Round the clock all day and (usu.) Night. [medieval latin clocca bell] 