a mechanical or electrical instrument that makes repeated clicking sounds at an adjustable pace, used for marking rhythm, especially in practicing music.
Origin: 1810–20;metro-1 + -nome < Greeknómos rule, law
a mechanical device which indicates the exact tempo of a piece of music by producing a clicking sound from a pendulum with an adjustable period of swing
[C19: from Greek metron measure + nomos rule, law]
1816, coined in Eng. from comb. form of Gk. metron "measure" (see meter (2)) + -nomos "regulating," verbal adj. of nemein "to regulate" (see numismatics). The device invented 1815 by John Maelzel.