Open English Wordnet
Adjectives
(s)clandestine, cloak-and-dagger, hole-and-corner, hugger-mugger, hush-hush, secret, surreptitious, undercover, undergroundconducted 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”