1. clandestine, cloak-and-dagger, hole-and-corner, hugger-mugger, hush-hush, secret, surreptitious, undercover, underground

conducted with or marked by hidden aims or methods

Example Sentences:
'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'

Synonyms

• clandestine
• cloak-and-dagger
• hole-and-corner
• hugger-mugger
• hush-hush
• secret
• surreptitious
• underground