| clandestine(adjective, secret, unknown, hidden, sly) |
| secret(adjective, unknown, hidden, spy, concealed) |
| subway(noun, american, railroad) |
| buried(verb, adjective, secret, unknown, hidden) |
| tube |
| covert(adjective, secret, unknown, hidden, concealed) |
| surreptitious(adjective, secret, unknown, hidden, concealed) |
| undercover(adjective, secret, unknown, hidden, spy) |
| subterranean(adjective, surface, depth) |
| metro |
| resistance(noun, resist) |
| covered(adjective, obscure, unknown, hidden, concealed) |
| hidden(verb, adjective, secret, unknown, concealed) |
| concealed(adjective, secret, unknown, hidden, spy) |
| hole-and-corner(adjective, secret, hidden, spy, covert) |
| secretly(adverb, undercover) |
| cloak-and-dagger(adjective, obscure, unknown, hidden, clandestine) |
| furtive(adjective, obscure, secret, unknown, hidden) |
| hush-hush(adjective, secret, hidden, spy, clandestine) |
| hugger-mugger |