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 in Canada) a hydroelectric power company or board

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hydro ³ British  

/ ˈhaɪdrəʊ /

noun

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

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hydro- ⁴ 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– 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 ( -o ); hydro ( def. 4 ) hydro- ¹ analyzed as an adj.

Origin of hydro-²

< Greek, combining form of hýdōr water

Example Sentences

In the pitch black of the mine, mud-splattered men with headlamps drill into the rock in two-man teams, using hydro drills with long, thin nozzles that shoot out pressurized water to loosen the ore.

From The Wall Street Journal • Jan. 27, 2026

Ecuador, a country of 17 million, relies on hydro generation for 70 percent of its electric power.

From Barron's • Jan. 22, 2026

They do not include smaller-scale gas, biomass and hydro operators feeding in electricity at a local level, but these contribute a relatively small fraction of Britain's total generation.

From BBC • Jan. 2, 2026

Based in Baltimore, the company is the largest producer of carbon-free energy in the U.S., with most of its output coming from hydro, wind, solar and nuclear.

From The Wall Street Journal • Dec. 22, 2025

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