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• hydro
  hydro

  noun

  hydroelectric power.
• hydro-
  hydro-

  a combining form meaning “water,” used in the formation of compound words.
• Hydro
  Hydro

  noun

  (esp in Canada) a hydroelectric power company or board
• hydro–
  hydro–

  A prefix that means: “water” (as in hydroelectric) or “hydrogen,” (as in hydrochloride).

hydro

¹ American  

[hahy-droh] / ˈhaɪ droʊ /

noun

plural

hydros

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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adjective

1. Informal. of, relating to, or furnishing water, water power, or hydroelectricity.

   funds for new hydro projects.

hydro- ² American  

1. a combining form meaning “water,” used in the formation of compound words.

   hydroplane; hydrogen.

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hydro- ³ American  

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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hydro ¹ British  

/ ˈhaɪdrəʊ /

adjective

1. short for hydroelectric

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noun

1. a Canadian name for electricity when it is supplied to a residence, business, institution, etc

hydro ² British  

/ ˈhaɪdrəʊ /

noun

1. (esp formerly) a hotel or resort, often near a spa, offering facilities for hydropathic treatment

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hydro- ³ British  

combining form

1. indicating or denoting water, liquid, or fluid

   hydrolysis

   hydrodynamics

2. indicating the presence of hydrogen in a chemical compound

   hydrochloric acid

3. indicating a hydroid

   hydrozoan

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Hydro ⁴ British  

/ ˈhaɪdrəʊ /

noun

1. (esp in Canada) a hydroelectric power company or board

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hydro– Scientific  

1. A prefix that means: “water” (as in hydroelectric) or “hydrogen,” (as in hydrochloride).

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Usage

What does hydro- mean? Hydro- is a combining form used like a prefix that has two distinct senses. The first of these senses is “water,” and this form of hydro- is often used in a variety of scientific and technical terms. Hydro- comes from Greek hýdōr, meaning “water.”The second of these senses is “hydrogen,” and this form of hydro- is occasionally used in a variety of scientific terms, especially in chemistry. Hydrogen, the lightest of the elements, combines with oxygen to form water. The word hydrogen comes from French hydrogène. The suffix -gen, or its equivalent in French, means "that which produces." Hydrogen literally translates to "that which produces water."What are variants of hydro-?When combined with words or word elements that begin with a vowel, hydro- becomes hydr-, as in hydrant. Want to know more? Read our Words That Use article on hydr-.

Etymology

Origin of hydro¹

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

Origin of hydro-²

< Greek, combining form of hýdōr water

Example Sentences

“I will advance renewable energy, import less foreign fuel and stop decommissioning of hydro and nuclear power. However, many current initiatives have unintended consequences, and my plan focuses on incentives, not mandates,” she said.

From Los Angeles Times • May 1, 2026

Much of that weak performance has to do with lower hydro generation, RBC’s Alexander Wheeler and Ziyad Jasimuddin write in a note.

From The Wall Street Journal • Mar. 18, 2026

This is supported by record high hydro reserves—energy which hasn’t been sold yet—of 9 Terawatt hours.

From The Wall Street Journal • Feb. 26, 2026

In 2025, Alphabet approached Brookfield Renewable to secure three gigawatts of hydro power External link.

From Barron's • Feb. 18, 2026

Mahipar—which means “Flying Fish”—was a high summit with a precipitous drop overlooking the hydro plant the Germans had built for Afghanistan back in 1967.

From "The Kite Runner" by Khaled Hosseini