(a.) Conducted with secrecy; surreptitious\; withdrawn from public notice, usually for an evil purpose; kept secret; hidden; private; underhand; as, a clandestine marriage.

back-door backstairs covert feline furtive hidlings hole-and-corner hugger-mugger privy quiet shifty skulking slinking slinky sly sneaking sneaky stealthy surreptitious under-the-counter under-the-table undercover underground underhand underhanded unobtrusive