| 1. clandestine, concealed, spying. undercover 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 [syn: clandestine, cloak-and-dagger, hole-and-corner(a) , hugger-mugger, hush-hush, on the quiet(p) , secret, surreptitious, underground] |