Conducted with or marked by hidden aims or methods. Synonyms: clandestine, cloak-and-dagger, hole-and-corner, hugger-mugger, hush-hush, secret, surreptitious, underground. "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"
