surreptitious Synonyms

furtive underground sneaky secret stealthy cloak-and-dagger hole-and-corner hush-hush hugger-mugger clandestine sneak undercover private sneaking treacherous ulterior sly subterrestrial underhand underhanded unrevealed under cover unavowed conspiratorial under-the-table sub-rosa behind-the-scenes wily veiled under false pretense slinky slinking skulking devious deceitful cunning crafty covinous covert confidential concealed closet backstairs backhanded disguised fraudulent sideways sidelong shrouded shifty