flagrantly Antonyms
adorably
collusively
conspiratorially
discreetly
on the q.t.
on the qt
on the side
on the sly
unassailably
under the counter
unimpeachably
unobserved
behind one's back
in a quiet way
in a secret
in a secretive manner
clandestinely
behind someone's back
behind closed doors
calmly
confidentially
covertly
deliberately
furtively
privately
privily
quietly
secretly
slyly
stealthily
warily
sub-rosa
in secret
in private
in a secretive way