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

There, a permanent shadow is thought to shroud an area abundant with water ice – a valuable resource that could be extracted and used for drinking, breathing and as a source of hydrogen and oxygen for rocket fuel. —Eric Lagatta, USA Today, 30 Mar. 2026

Deuterium can replace one or both of the ordinary hydrogen atoms in water, which is what scientists mean by deuterium enrichment. —Keith Cooper, Space.com, 30 Mar. 2026

The core stage of the SLS rocket will be filled with 537,000 gallons of supercold liquid hydrogen fuel and 196,000 gallons of liquid oxygen. —William Harwood, CBS News, 30 Mar. 2026

These isotopic measurements, including ratios involving hydrogen, nitrogen, and sulfur, are essential for reconstructing the planet’s history, such as the loss of water over time and ongoing chemical cycles within the atmosphere. —Prabhat Ranjan Mishra, Interesting Engineering, 30 Mar. 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