underground

1 of 3

adverb

un·​der·​ground ˌən-dər-ˈgrau̇nd 

1

: beneath the surface of the earth

2

: in or into hiding or secret operation

underground

2 of 3

noun

ˈən-dər-ˌgrau̇nd 

1

: a subterranean space or channel

2

: an underground city railway system

3

a

: a movement or group organized in strict secrecy among citizens especially in an occupied country for maintaining communications, popular solidarity, and concerted resistive action pending liberation

b

: a clandestine conspiratorial organization set up for revolutionary or other disruptive purposes especially against a civil order

c

: an unofficial, unsanctioned, or illegal but informal movement or group

especially : a usually avant-garde group or movement that functions outside the establishment

underground

3 of 3

adjective

un·​der·​ground ˈən-dər-ˌgrau̇nd 

1

: being, growing, operating, or situated below the surface of the ground

2

: conducted by secret means

3

a

: existing outside the establishment

an underground literary reputation

b

: existing outside the purview of tax collectors or statisticians

the underground economy

4

a

: produced or published outside the establishment especially by the avant-garde

underground movies

underground newspapers

b

: of or relating to the avant-garde underground

an underground moviemaker

an underground theater

Synonyms of underground

Noun

• resistance

Adjective

• clandestine
• undercover
• covert
• sneak
• private

Examples of underground in a Sentence

Adverb

They had been living underground as fugitives.

Noun

I've ridden on the New York subway, the Paris Metro, and the London Underground.

joined the underground while still a teenager

Adjective

The drugs are supplied through an underground network.

She loves the city's underground music scene.

Recent Examples on the Web

Adverb

That means, depending on the particular lake, the water might be filtering through limestone underground before emerging, or the bottom of the lake might be mostly limestone, not squishy mud. —Kaitlyn Yarborough, Southern Living, 13 Mar. 2026

For years now, that’s pretty much what has been happening in the section of hip-hop’s underground that treats Whole Lotta Red like a sacred text—just replace the Western desert with Discord chats. —Alphonse Pierre, Pitchfork, 13 Mar. 2026

Noun

His father was forged by years of revolutionary hardship—prison, persecution, life underground—before coming to power and reportedly amassing a war chest exceeding $100 billion, built in part from properties confiscated from religious minorities who fled persecution. —Karim Sadjadpour, The Atlantic, 10 Mar. 2026

Bunn had previously used AI to search for new sources of oil underground, but pivoted to medical work after his wife had a series of miscarriages. —Meg Wingerter, Denver Post, 4 Mar. 2026

Adjective

Since then, Tehran has fortified Kharg heavily, building air defenses, hardened infrastructure and underground storage designed to keep oil flowing even under sustained attack. —Imtiaz Tyab, CBS News, 14 Mar. 2026

Parking would be underground and at street level, with 24/7 valet service. —Erika I. Ritchie, Oc Register, 14 Mar. 2026

Word History

First Known Use

Adverb

1598, in the meaning defined at sense 1

Noun

1594, in the meaning defined at sense 1

Adjective

1601, in the meaning defined at sense 1

Phrases Containing underground

• go underground
• the underground

Rhymes for underground

• aboveground
• battleground
• belowground
• paperbound
• turnaround
• ultrasound
• wraparound
• abound
• aground
• around
• astound
• background

Kids Definition

underground

1 of 3 adverb

un·​der·​ground ˌən-dər-ˈgrau̇nd 

1

: below the surface of the ground

an underground passage

2

: in or into hiding or secret operation

the political party went underground

underground

2 of 3 noun

un·​der·​ground

ˈən-dər-ˌgrau̇nd

1

: a space under the surface of the ground

especially : subway sense 2

2

: a secret political group

especially : an organized body working in secret to overthrow a government or an occupying power

underground

3 of 3 adjective

un·​der·​ground ˈən-dər-ˌgrau̇nd 

1

: being, growing, operating, or located below the surface of the ground

an underground stream

2

: conducted secretly