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