Undercover
WordNet
adjective
(1) 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"
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