Synonyms of undercover in English:

undercover


See definition of undercover

adjective

1‘they were arrested after a three-year undercover investigation’

SYNONYMS
covert, secret, clandestine, private, confidential, conspiratorial, underground, surreptitious, furtive, cloak-and-dagger, hole-and-corner, hugger-mugger, back-alley, backstair, stealthy, closet
intelligence
hidden, concealed, masked, veiled, shrouded
black
informal hush-hush, sneaky
ANTONYMS

open, overt