hush-hush
1. [ adjective ] conducted with or marked by hidden aims or methods
Synonyms: secret clandestine undercover underground on_the_quiet hugger-mugger surreptitious hole-and-corner cloak-and-dagger
Examples:

"clandestine intelligence operations" "cloak-and-dagger activities" "secret missions" "surreptitious mobilization of troops" "an undercover investigation" "underground resistance"

Related terms: covert
Similar spelling:   hughes