• synonyms


noun, plural hy·dros for 2, 3.
  1. Informal. hydroelectric power.
  2. Informal. hydroplane.
  3. British.
    1. a bathhouse, hotel, or resort catering to people taking mineral-water health cures; spa.
    2. an establishment furnishing hydrotherapy.
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  1. Informal. of, relating to, or furnishing water, water power, or hydroelectricity: funds for new hydro projects.
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Origin of hydro

1880–85; by shortening of compounds with hydro-1 (cf. -o); (def 4) hydro-1 analyzed as an adj.


  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


  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

Examples from the Web for hydro

Historical Examples

  • Hydro: relating to water: a combining form used as a prefix.

    Explanation of Terms Used in Entomology

    John. B. Smith

  • The Norfolk suit and the false moustache are in her room at the hydro.

  • This is done in a kind of wringing machine called a "hydro extractor."

  • Harbrace and the hydro engineer jumped for the communications phone.

  • Designed to be used also as a hydro, with three step floats.

British Dictionary definitions for hydro


noun plural -dros
  1. British (esp formerly) a hotel or resort, often near a spa, offering facilities for hydropathic treatment
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  1. short for hydroelectric
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  1. a Canadian name for electricity when it is supplied to a residence, business, institution, etc
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  1. (esp in Canada) a hydroelectric power company or board
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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

short for hydroelectric, from 1916.

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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


  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


  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.