underground:1

adverb
un*der*ground \ ˌən-dər-ˈgrau̇nd \
14th century{ds||1||}
  • beneath the surface of the earth
  • in or into hiding or secret operation

underground:2

noun
underground \ ˈən-dər-ˌgrau̇nd \
1594{ds||1||}
  • a subterranean space or channel
  • an underground city railway system
  • 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

underground:3

adjective
un*der*ground \ ˈən-dər-ˌgrau̇nd \
1601{ds||1||}
  • being, growing, operating, or situated below the surface of the ground
  • conducted by secret means
  • existing outside the establishment

Underground Railroad

noun
Underground Railroad \
1842
  • a system of cooperation among active antislavery people in the U.S. before 1863 by which people escaping enslavement were secretly helped to reach the North or Canada

go underground

idiom
go underground \
  • to start working in secret

the underground

noun
the underground \
  • a group of people who secretly work to oppose or overthrow a government
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