Answer: UNDERGROUND

AnswerCrossword Clue
UNDERGROUNDSecret revolutionary force
UNDERGROUNDClandestine group
UNDERGROUNDBlitz shelter
UNDERGROUNDEscaping detection
UNDERGROUNDLondon subway.
UNDERGROUNDMaquis, for instance.
UNDERGROUNDBritish subway system
UNDERGROUNDLondon transportation
UNDERGROUNDLike Tubman's railroad
undergrounda subterranean space or channel
undergroundIn or into secrecy or hiding, esp. as a result of carrying out subversive political activities
undergroundBeneath the surface of the ground