privily
Secretly, in secret; in a private manner; privately.
archaic
King Edward: I dare not, for the people love him well. Gaveston: Why, then we'll have him privily made away.
Gaveston: Why do you not commit him to the Tower?
Where it comes from
From Middle English prively; equivalent to privy + -ly.
Adapted from the Wiktionary entry privily (CC BY-SA 4.0).