Undercover

Adjective

 * 1) Performed or happening in secret.
 * 2) Employed or engaged in spying or secret investigation.

Noun

 * 1) A person who works undercover.

Synonyms

 * clandestine

Thesaurus
above water, abstruse, armored, at anchor, back-door, backstairs, beclouded, behind the curtain, behind the scenes, behind the veil, blind, buried, cased, ceiled, clandestine, cloaked, close, clouded, coated, concealed, confidential, coped, covered, covert, covertly, cowled, curtained, doggo, eclipsed, encapsulated, encapsuled, encased, enveloped, enwrapped, feline, filmed, floored, furtive, hid, hidden, hidden out, hidlings, high and dry, hole-and-corner, hooded, housed, hugger-mugger, hush-hush, in a cloud, in a corner, in a fog, in a whisper, in ambush, in darkness, in eclipse, in harbor, in hiding, in hidlings, in purdah, in safety, in secret, in the background, in the clear, in the dark, in the wings, incommunicado, latent, loricate, loricated, lurking, mantled, masked, muffled, mysterious, nobody the wiser, obfuscated, obscure, obscured, occult, occulted, on, on tiptoe, out of danger, packaged, past danger, paved, private, privy, prowling, pussyfoot, pussyfooted, quiet, recondite, roofed-in, screened, scummed, secluded, secluse, secret, secretly, sequestered, sheathed, shelled, shielded, shifty, shrouded, skulking, slinking, slinky, sly, sneaking, sneaky, sotto voce, stealing, stealthy, sub rosa, surreptitious, swathed, tented, terra firma, under an eclipse, under cover, under house arrest, under the breath, under the rose, under wraps, under-the-counter, under-the-table, underground, underhand, underhanded, underneath, unknown, unobtrusive, veiled, waiting concealed, walled, walled-in, with bated breath, wrapped, wrapped in clouds