under cover (adjective) undercover: secret, spy
Sinonime: clandestine,
concealed,
confidential,
covert,
creep,
furtive,
hidden, hole-and-corner, hush-hush,
incognito*,
intelligence, on the QT,
private,
stealth,
stealthy, sub-rosa,
surreptitious, under wraps,
underground, underhand, underneath
Antonime: known,
open,
public