done secretly; kept secret
secret, sly
(of glances, threats etc) hidden; disguised
clandestine, underhanded
done secretly so as not to attract attention
sneaky, secretive
(that is to be) kept from the knowledge or view of others; of which others have no knowledge
hidden, unrevealed
underground
hidden, underground
(of actions) done secretly
sneaky, secret
beyond what is first seen or said
secret; pertaining to a hidden goal
acting secretly
secret, spy
deceitful(ly)
deceitful