tapper

noun8

1. •
   One who makes a tapping noise.

   • A low tap was heard at the room door. Mr. Bob Sawyer looked expressively at his friend, and bade the tapper come in[…] — 1836
2. •
   A tap-dancer.
3. •
   A wiretapper.
4. •
   (slang) A weakly hit ground ball.
5. •
   An assistant in the sport of paraswimming who taps blind or visually impaired swimmers with a pole to indicate when they should turn around.
6. •
   (US) A tapster.
7. •
   (dialect, UK) The lesser spotted woodpecker.
8. •
   In early wireless telegraphs, a device used to shake loose the filings of a coherer.