Synonyms of underground

underground 1 of 3

adjective

ˈən-dər-ˌgrau̇nd 

1

as in clandestine

undertaken or done so as to escape being observed or known by others

an underground operation to smuggle ancient artifacts out of the country

Synonyms & Similar Words

• clandestine
• undercover
• covert
• sneak
• private
• sneaking
• stealth
• secret
• surreptitious
• furtive
• stealthy
• behind-the-scenes
• hole-and-corner
• sneaky
• underhanded
• undisclosed
• backstairs
• underhand
• privy
• subterranean
• hush-hush
• confidential
• hidden
• off-the-books
• closed-door
• hugger-mugger
• classified
• secreted
• restricted
• off-the-record
• top secret
• concealed
• unexposed
• back-channel
• unadvertised

Antonyms & Near Antonyms

• public
• open
• overt
• avowed
• acknowledged
• straightforward
• unrestricted
• unclassified
• obvious
• evident
• clear
• plain
• manifest
• undisguised
• unconcealed
• aboveboard
• patent

2

as in subterranean

being, situated, or operating beneath the surface of the earth

an underground shopping mall that is part of the city's subway system

Synonyms & Similar Words

• subterranean
• subsurface
• belowground

Antonyms & Near Antonyms

• surface
• aboveground

underground

2 of 3

noun

ˈən-dər-ˌgrau̇nd 

as in resistance

a secret organization in a conquered country fighting against enemy forces

joined the underground while still a teenager

Synonyms & Similar Words

• resistance
• conspiracy
• cabal

underground

3 of 3

adverb

as in undercover

Related Words

• undercover
• stealthily
• surreptitiously
• clandestinely
• secretively
• furtively
• covertly
• underhanded
• sneakily
• underhand
• underhandedly
• offstage
• collusively
• conspiratorially
• offscreen
• à deux
• inwardly
• sotto voce
• tête-à-tête
• secretly
• privately
• backstage
• intimately
• confidentially
• in camera

Dissimilar Words

• publicly
• openly

Example Sentences

Recent Examples of underground

Adjective

Dig It Up Since lily of the valley spreads via underground rhizomes, the most effective removal method is to dig up the plant and dispose of it. — Helena Madden, Martha Stewart, 20 July 2026

The United States conducted a new round of airstrikes early today targeting Iran after announcing the death of another American service member, hitting around a northwestern city believed to be home to underground missile bases. — Chicago Tribune, 20 July 2026

Noun

Invisible hands strap her legs onto the stirrups, an iron fist plunging her through a tunneling, gravity‑bending, black underground. — Literary Hub, 25 June 2026

The company now plans to demonstrate commercial-scale borehole drilling before attempting deployment of a prototype reactor underground. — Aamir Khollam, Interesting Engineering, 24 June 2026

Adverb

In the monitoring room, screens blinked and maps pulsed, quietly charting what was happening underground. — Andrei Popoviciu, The Dial, 21 July 2026

The crowd is packed not only with devoted fans and freaks, but fellow musicians who also emerged from the punk rock underground decades earlier. — Steve Appleford, SPIN, 20 July 2026