[1] : WordNet (r) 2.0

undercover
     adj : conducted with or marked by hidden aims or methods;
           "clandestine intelligence operations";
           "cloak-and-dagger activities behind enemy lines";
           "hole-and-corner intrigue"; "secret missions"; "a
           secret agent"; "secret sales of arms"; "surreptitious
           mobilization of troops"; "an undercover investigation";
           "underground resistance" syn: clandestine, cloak-and-dagger,
            hole-and-cornera, hugger-mugger, hush-hush, on
           the quietp, secret, surreptitious, underground
see also:
clandestine cloak-and-dagger hole-and-cornera hugger-mugger hush-hush on the quietp 
secret surreptitious underground 

[2] : Moby Thesaurus II by Grady Ward, 1.0

141 moby thesaurus words for "undercover":
   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

Undercover >> U Words
Undercover, definition of term: Undercover
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