underground Synonyms

secret belowground clandestine covert furtive surreptitious stealthy sneaky undercover hidden hugger-mugger subsurface hush-hush hole-and-corner resistance subterranean subterraneous cloak-and-dagger concealed nonpublic backroom back channel unconventional saboteur public transport avant-garde unacknowledged metro resistor public transit maquis passenger train black-market shadow gray market maquisard under-the-table behind-the-scenes maglev below ground fifth column underground press in the earth into hiding subways below ground level underground economy underground network underground organization underground press outlet