hydro- 1
a combining form meaning "water," used in the formation of compound words: hydroplane; hydrogen.
Also, esp. before a vowel, hydr- 1 .
[ hýdor water ]
hydro- 2
a combining form representing hydrogen in compound words, denoting esp. a combination of hydrogen with some negative element or radical: hydrobromic.
Also, esp. before a vowel, hydr- 2 .