metronome (n.)
mechanical musical time-keeper, 1815, coined in English from comb. form of Greek metron "measure" (see meter (n.2)) + -nomos "regulating," verbal adjective of nemein "to regulate" (see numismatic). The device invented 1815 by Johann Maelzel (1772-1838), German civil engineer and showman. Related: Metronomic.