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Hydr– is a combining form used like a prefix that has two distinct senses.

The first of these senses is “water,” and this form of hydr– is often used in a variety of scientific and technical terms. Hydr– comes from Greek ��ý��ō��, meaning “water.”

The second of these senses is “hydrogen,” and this form of hydr– 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 the 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 hydr-?

Hydr– is a variant of hydro–, which loses its –o– when combined with words or word elements beginning with vowels. Want to know more? Read our �������t¶��s That Use article on hydro-.

Not every word that begins with the exact letters hydr-, such as hydranth or hydroid, is necessarily using the combining form hydr– to denote “water” or “hydrogen.” Learn why hydroid means “hydra-like” at our entry for the word.

A scientific term that features the form hydr– you may have come across is hydrate, “any of a class of compounds containing chemically combined water.”

The hydr– part of the word means “water,” as we have seen. The suffix –ate is used in terms from chemistry to indicate the stem of an element or group. Hydrate is the name of the group of elements containing water.

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

• hydrant
• hydrarch
• hydrase
• hydrops (using the equivalent form of hydr– in Greek)
• hydrous

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

• hyal-
• hyp-

Break it down!

The suffix –ous means “possessing” or “full of.” With this in mind, what does hydrous mean?

One example of a term from chemistry that uses hydr– to represent “hydrogen” is hydride, “a binary compound formed by hydrogen and another, usually more electropositive, element or group.”

The hydr– part of the word here means “hydrogen.” The suffix –ide is used in the name of chemical compounds. Hydride literally means “chemical compound [with] hydrogen.”

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

• hydracid
• hydric
• hydriodic
• hydriodic acid

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

• hyal-
• hyp-

Break it down!

The term from chemistry iodic means “containing iodine.” With this in mind, what does hydriodic mean?