Conducted with or marked by hidden aims or methods:
— Clandestine intelligence operations.

synonyms: cloak-and-dagger, hole-and-corner, hugger-mugger, hush-hush, secret, surreptitious, undercover, underground.

Roget 528: concealed etc. v.; hidden; secret, recondite, mystic, cabalistic, occult, dark; cryptic, cryptical^†; private, privy, in petto, auricular, clandestine, close, inviolate; tortuous.    behind a screen etc. 530; undercover, under an eclipse; in ambush, in hiding, in disguise; in a cloud, in a fog, in a mist, in a haze, in a dark corner; in the shade, in the dark; clouded, wrapped in clouds, wrapt in clouds^†; invisible etc. 447; buried, underground, perdu [Fr.]; secluded etc. 893.    undisclosed etc. 529, untold etc. 527; covert etc. (latent) 526; untraceable; mysterious etc. (unintelligible) 519.    irrevealable^†, inviolable; confidential; esoteric; not to be spoken of; unmentionable.    obreptitious^†, furtive, stealthy, feline; skulking etc. v.; surreptitious, underhand, hole and corner; sly etc. (cunning) 702; secretive, evasive; reserved, reticent, uncommunicative, buttoned up; close, close as wax; taciturn etc. 585.    ... show more