a combining form meaning “water,” used in the formation of compound words: hydroplane; hydrogen.

Nearby words

  1. hydride,
  2. hydrilla,
  3. hydriodic,
  4. hydriodic acid,
  5. hydro,
  6. hydro-lyase,
  7. hydro-ski,
  8. hydroa,
  9. hydroa vacciniforme,
  10. hydroacoustics

Also especially before a vowel, hydr-1.

Origin of hydro-

< Greek, combining form of hýdōr water



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.

Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

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

Word Origin and History for hydro-


before vowels hydr-, word-forming element meaning "water," from Greek hydro-, comb. form of hydor "water" (see water (n.1)). Also sometimes a comb. form of hydrogen.

Online Etymology Dictionary, © 2010 Douglas Harper

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.