underground
UK: ˌʌndəˈɡraʊnd | US: ˌʌndərˈɡraʊnd
adj. situated beneath the surface of the ground
adj. secret; operating secretly or illegally
n. a subterranean space or passage
n. a secret group or movement, especially in resistance
The word "underground" combines the Old English prefix "under-" (meaning "below") with "ground" (from Old English "grund," meaning "earth" or "soil"). Originally literal, it evolved metaphorically in the 17th century to describe secret activities, influenced by mining terminology and later political resistance movements.
The subway runs underground to avoid traffic.
The rebels organized an underground network to distribute banned literature.
Archaeologists discovered an ancient underground chamber.
The band gained fame in the underground music scene before going mainstream.
Some animals build elaborate underground burrows for shelter.