Wordnet 3.0
ADJECTIVE (1)
1. 
 conducted with or marked by hidden aims or methods; 
- Example: "clandestine intelligence operations"- Example: "cloak-and-dagger activities behind enemy lines"- Example: "hole-and-corner intrigue"- Example: "secret missions"- Example: "a secret agent"- Example: "secret sales of arms"- Example: "surreptitious mobilization of troops"- Example: "an undercover investigation"- Example: "underground resistance"[syn: clandestine, cloak-and-dagger, hole-and-corner(a), hugger-mugger, hush-hush, secret, surreptitious, undercover, underground]
WordNet (r) 3.0 (2006):
cloak-and-dagger
    adj 1: 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, secret,
           surreptitious, undercover, underground]