metronome(n = noun.artifact) - clicking pendulum indicates the exact tempo of a piece of music;
is a kind of pendulum
An instrument consisting of a short pendulum with a sliding weight. It is set in motion by clockwork, and serves to measure time in music. [1913 Webster]
metronome, n. Mus. an instrument marking time at a selected rate by giving a regular tick.
Derivative:
metronomic adj.
Etymology:
Gk metron measure + nomos law