Synset

conducted with or marked by hidden aims or methods
<adj.all>   (a)   freq. cnt.: 4 freq. cnt.: 2 freq. cnt.: 1 freq. cnt.: 1

clandestine

cloak-and-dagger

hole-and-corner

hugger-mugger

hush-hush

secret

surreptitious

undercover

underground

sample 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"