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 compare deuterium, tritium

hydrogenous

hī-ˈdrä-jə-nəs 

adjective

Examples of hydrogen in a Sentence

Recent Examples on the Web

By studying the region with narrowband filters sensitive to hydrogen (H-alpha) and sulfur (S II) emissions, the team detected a coherent, circular shell structure centered on the nova. —Rupendra Brahambhatt, Interesting Engineering, 27 Sep. 2025

That's where water ice thought to be abundant in the region could be extracted and used for drinking, breathing and as a source of hydrogen and oxygen for rocket fuel. —Eric Lagatta, USA Today, 25 Sep. 2025

The $97 million Carruthers mission carries two co-aligned ultraviolet imagers designed for simultaneous observations of Earth's exosphere, a tenuous cloud of hydrogen gas that fades into the airless void of outer space about halfway to the Moon. —Kyle Orland, ArsTechnica, 24 Sep. 2025

Among the companies on the list is Deloitte, which recently helped Brazil develop hydrogen power by creating a model to work across various supply-chain scenarios, for example. —Sheryl Estrada, Fortune, 24 Sep. 2025

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

• 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