Webster's Revised Unabridged Dictionary · 1913

Hydro

Hydro , noun

1.
A hydro-aeroplane. [obsolescent]
2.
hydroelectric power; -- also used attributively.

Hydro-

1.
A combining form from Greek {not transcribed}, {not transcribed}, water (see Hydra).
2.
(Chemistry) A combining form of hydrogen, indicating hydrogen as an ingredient, as hydrochloric; or a reduction product obtained by hydrogen, as hydroquinone.

Also: Hydr-