hydrogen

noun

hy·​dro·​gen ˈhī-drə-jən 

-dər-

: a nonmetallic gaseous chemical element with atomic number 1 that is the simplest and lightest of the elements and that is used especially in the processing of fossil fuels and the synthesis of ammonia

—often used before another noun

hydrogen gas

hydrogen atoms

a hydrogen vehicle

the hydrogen industry

see Chemical Elements Table see also green hydrogen compare deuterium, tritium

hydrogenous

hī-ˈdrä-jə-nəs 

adjective

Examples of hydrogen in a Sentence

Recent Examples on the Web

The former Scottish oil capital has suffered thousands of job losses and economic stagnation following the oil industry’s decline and has struggled to build the same momentum in offshore wind and hydrogen. — Heather Farmbrough, Forbes.com, 30 June 2026

While there is a growing number of zero-emissions heavy-duty vehicles, including both battery EVs and hydrogen fuel cell EVs, adoption lags behind light-duty passenger vehicles. — Jonathan M. Gitlin, ArsTechnica, 30 June 2026

The process of transferring cryogenic fluid in a vacuum is highly difficult, especially when handling liquid hydrogen and liquid oxygen. — Mrigakshi Dixit, Interesting Engineering, 30 June 2026

Meanwhile, billionaires are investing in hydrogen and fusion. — U T Readers, San Diego Union-Tribune, 29 June 2026

Word History

Etymology

French hydrogène, from hydr- + -gène -gen; from the fact that water is generated by its combustion

First Known Use

1788, in the meaning defined above

Phrases Containing hydrogen

• green hydrogen
• heavy hydrogen
• hydrogen bomb
• hydrogen bond
• hydrogen bromide
• hydrogen chloride
• hydrogen cyanide
• hydrogen fluoride
• hydrogen iodide
• hydrogen ion
• hydrogen peroxide
• hydrogen sulfide

Rhymes for hydrogen

• dihydrogen

Kids Definition

hydrogen

noun

hy·​dro·​gen ˈhī-drə-jən 

: a chemical element that is the simplest and lightest of all chemical elements and is normally found alone as a colorless odorless highly flammable gas having two atoms per molecule see element

hydrogenous

hī-ˈdräj-ə-nəs 

adjective

Etymology

from French hydrogène "hydrogen," from hydr- "water" and -gène "producer"; so called because when hydrogen gas burns, it combines with oxygen to produce water

Medical Definition

hydrogen

noun

hy·​dro·​gen ˈhī-drə-jən 

: a nonmetallic element that is the simplest and lightest of the elements and that is normally a colorless odorless highly flammable diatomic gas

—symbol H see deuterium, tritium Chemical Elements Table

hydrogenous

hī-ˈdräj-ə-nəs 

adjective