in petto
under the rose
close-tiled
in secret
on the hush
off-the-record
hugger-mugger
underground
privately
intimate
homely
closehanded
esoteric
on the down-low
secretly
under the covers
latently
subterranean
confide
have a word in someone's ear
have a quiet word
concealedly
confidentiality
in confidence
eavesdropping
private
sub rosa
darkness
auricular
on the Q.T.
out of sight
in hiding
secret
doggo
behind the scenes
covertly
off the grid
under the table
tête-à-tête
keep a lid on
cryptadia
privily
cloakedly
in camera
closehandedness
secernent
closeness
on the QT
closet
snoop