metronome (n.) Look up metronome at Dictionary.com
mechanical musical time-keeper, 1815, coined in English from Greek metron "measure" (from PIE root *me- (2) "to measure") + -nomos "regulating," verbal adjective of nemein "to regulate" (from PIE root *nem- "assign, allot; take"). The device invented 1815 by Johann Maelzel (1772-1838), German civil engineer and showman. Related: Metronomic.