One who makes a tapping noise.

A tap-dancer.

A phone tapper or wiretapper.

(baseball slang) A weakly hit ground ball.

(telegraphy) In early wireless telegraphs, a device used to shake loose the filings of a coherer.

(US) A tapster.

(sports) An assistant in the sport of paraswimming who taps blind or visually impaired swimmers with a pole to indicate when they should turn around.