Webster’s Revised Unabridged Dictionary · 1913
Hydro-
Hy′dro- (hī′drō·), Hy′dr-. 1. A combining form from Gr. ὕδωρ, ὕδωρ, water (see Hydra).
2. (Chem.) A combining form of hydrogen, indicating hydrogen as an ingredient, as hydrochloric; or a reduction product obtained by hydrogen, as hydroquinone.