The Collaborative International Dictionary
Hydr-
Hydr- \Hy"dr-\ See under Hydro-.
Hydr-
Hydro- \Hy"dro-\, Hydr- \Hy"dr-\
A combining form from Gr. ?, ?, water (see Hydra).
(Chem.) A combining form of hydrogen, indicating hydrogen as an ingredient, as hydrochloric; or a reduction product obtained by hydrogen, as hydroquinone.
Wiktionary
hydr-
pre. (alternative form of hydro- lang=en nodot=1), used before a vowel.