on_the_quiet
1. [ adjective ] conducted with or marked by hidden aims or methods
Synonyms: secret clandestine undercover underground hush-hush 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:   on_the_QT
  on_the_qui_vive
  on_the_Q.T.
  on_the_spot
  on_the_side
  on_the_go
  on_the_sly
  on_the_job
  on_the_hook
  on_the_contrary