Xem thêm: clandestine, cloak-and-dagger, hole-and-corner(a), hugger-mugger, secret, surreptitious, undercover, underground
adj.
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
