surreptitious
— Adjective
– English
~ 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"
surreptitious
— Adjective
– English
~ marked by quiet and caution and secrecy; taking pains to avoid being observed; "a furtive manner"; "a sneak attack"; "stealthy footsteps"; "a surreptitious glance at his watch"
surreptitiously
— Adverb
– English
~ in a surreptitious manner; "he was watching her surreptitiously as she waited in the hotel lobby"