UNDERCOVER
clandestine, cloak-and-dagger, hole-and-corner, hugger-mugger, hush-hush, secret, surreptitious, undercover, underground
(adjective) 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”
Source: WordNet® 3.1
Etymology
Adjective
undercover (comparative more undercover, superlative most undercover)
Performed or happening in secret.
Employed or engaged in spying or secret investigation.
Synonyms
• clandestine
• See also covert
Noun
undercover (plural undercovers)
A person who works undercover.
Verb
undercover (third-person singular simple present undercovers, present participle undercovering, simple past and past participle undercovered)
To provide too little coverage.
Source: Wiktionary