Harmonium n. : A musical instrument, resembling a small organ and especially designed for church music, in which the tones are produced by forcing air by means of a bellows so as to cause the vibration of free metallic reeds. It is now made with one or two keyboards, and has pedals and stops.

Example:
What's the difference between the accordion and Harmonium?

Taxonomy
harmonium, instrument, Indian harmonium, reeds, bellows, free reeds, stops, musical instrument, keyboard instrument, octave, Indian music, reed organ, shruti, keyboard, scale, hands, Indian, drone.

Defination from the web:
harmonium is a free-standing keyboard instrument similar to a reed organ. ... An added attraction of the harmonium in tropical regions was that the instrument held its tune regardless of heat and humidity, unlike the piano. ...