harmonium

noun2

1. •
   A small keyboard instrument that consists of a series of reed pipes, which sound when one of the keys is pressed to open a valve that allows air to pass through.

   • The only other man was a little grey-headed fellow with a pleasant face and quick, twinkling eyes, who sat at a harmonium in the corner. — 1925
2. •
   Synonym of Hooke's atom.