in secret
• without others knowing.
Similar:
secretly,
without anyone knowing,
in private,
privately,
in confidence,
confidentially,
behind closed doors,
behind the scenes,
behind someone's back,
under cover,
under the counter,
discreetly,
unobserved,
quietly,
furtively,
stealthily,
on the sly,
on the quiet,
privily,
conspiratorially,
covertly,
clandestinely,
on the side,
sub rosa,
in camera,
on the q.t.,
