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hydro-1

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

Origin of hydro-1

< Greek, combining form of hýdōr water

hydro-2

  1. a combining form representing hydrogen in compound words, denoting especially a combination of hydrogen with some negative element or radical: hydrobromic.
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Also especially before a vowel, hydr-2.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

British Dictionary definitions for hydro-

hydro-

sometimes before a vowel hydr-

combining form
  1. indicating or denoting water, liquid, or fluidhydrolysis; hydrodynamics
  2. indicating the presence of hydrogen in a chemical compoundhydrochloric acid
  3. indicating a hydroidhydrozoan
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Word Origin

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.

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Online Etymology Dictionary, © 2010 Douglas Harper

hydro- in Medicine

hydro-

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

hydro- in Science

hydro-

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