close-tiled
in petto
in secret
under the rose
on the hush
privately
esoteric
in camera
sub rosa
off-the-record
intimate
homely
closehanded
concealedly
tête-à-tête
private
cloakedly
under the covers
on the down-low
behind the scenes
darkness
confidentiality
privily
subterranean
hugger-mugger
on the Q.T.
secretly
on the QT
closeness
secernent
have a word in someone's ear
divulgence
divulgement
have a quiet word
confide
clandestinely
behind closed doors
occulted
out of sight
in hiding
doggo
under one's hat
cryptadia
à deux
lie low
confidentially
concealment
hiding
concealing
semisecrecy