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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 ��ý��ō��, 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 ������Dz�è�Ա�. 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 �������t¶��s That Use article on hydr-.

One example of a scientific term that features the form hydro– to mean “water” is hydrolysis, “chemical decomposition in which a compound is split into other compounds by reacting with water.”

We know hydro– means “water,” and the –lysis portion of the word refers to “release,” from Greek ��ý������. Hydrolysis literally translates to “water release.”

What are some words that use the combining form hydro-?

• hydrofoil
• hydrogen (using the equivalent form of hydro– in French)
• hydrology
• hydrophobia (using the equivalent form of hydro– in Greek)
• hydroplane
• hydrotropic

What are some other forms that hydro– may be commonly confused with?

• hyalo-
• hypo-

Break it down!

The combining form –logy is used to name areas of study or branches of science. With this in mind, what does hydrology mean?

A scientific term from chemistry that features the form hydro– to mean “hydrogen” is hydrochloric acid, “a colorless or faintly yellow, corrosive, fuming liquid, HCl, used chiefly in chemical and industrial processes.”

The hydro– part of hydrochloric here represents “hydrogen.” The –chloric part of the word means “of or containing chlorine in the pentavalent state.” Hydrochloric literally translates to “of or containing hydrogen and chlorine.”

What are some words that use the combining form hydro-?

• hydrobromic
• hydrocarbon
• hydrocyanic
• hydrodesulfurization
• hydrosulphate

What are some other forms that hydro– may be commonly confused with?

• hyalo-
• hypo-

Break it down!

A sulphate is a compound that contains sulphuric acid. With this in mind, what does the compound hydrosulphate contain?