a combining form meaning “water,” used in the formation of compound words: hydroplane; hydrogen.
Also especially before a vowel, hydr-1.

Origin of hydro-

< Greek, combining form of hýdōr water

Definition for hydro- (2 of 2)


a combining form representing hydrogen in compound words, denoting especially a combination of hydrogen with some negative element or radical: hydrobromic.
Also especially before a vowel, hydr-2.
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British Dictionary definitions for hydro-


sometimes before a vowel hydr-

combining form

indicating or denoting water, liquid, or fluidhydrolysis; hydrodynamics
indicating the presence of hydrogen in a chemical compoundhydrochloric acid
indicating a hydroidhydrozoan

Word Origin for hydro-

from Greek hudōr water
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Medicine definitions for hydro-



Water; liquid:hydrocephalus.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.

Science definitions for hydro-


A prefix that means: “water” (as in hydroelectric) or “hydrogen,” (as in hydrochloride).
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.