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

This is because, despite forming like stars from collapsing patches of overdense and cool gas, brown dwarfs fail to gather the mass needed to generate the temperatures and pressures in their cores needed to fuse hydrogen to helium. —Robert Lea, Space.com, 6 Mar. 2026

In December, Sustainable Energy Fund for Africa approved a $10 million loan to Hyphen Hydrogen Energy, a renewable energy firm producing hydrogen and ammonia in Namibia. —Arkansas Online, 5 Mar. 2026

How Peroxide Cleans Your Bathroom Hydrogen peroxide is a liquid containing hydrogen and oxygen molecules. —Nishaa Sharma, The Spruce, 5 Mar. 2026

Fire crews initially tried to extinguish the fire with water, but that created a new danger as the water and chemicals created flammable hydrogen gas. —Brandon Downs, CBS News, 5 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