All 3 Uses of

privy
in
Arrowsmith

Privily Clif complained to Martin, "Darn him, he acts like I was a worm.†
Chpt 3

Not once did he talk of results of the sort called "practical"; not once did he cease warring on the post hoc propter hoc conclusions which still make up most medical lore; not once did he fail to be hated by his colleagues, who were respectful to his face, uncomfortable in feeling his ironic power, but privily joyous to call him Mephisto, Diabolist, Killjoy, Pessimist, Destructive Critic, Flippant Cynic, Scientific Bounder Lacking in Dignity and Seriousness, Intellectual Snob, Pacifist, Anarchist, Atheist, Jew.†
Chpt 12

George William Vertigan insisted in debate, and afterward privily to Sir Robert Fairlamb, that rats destroy food and perhaps spread disease, and His Excellency must veto the bill.†
Chpt 31 *

Definitions:

(1) (privy as in: privy to her real identity)
informed about something secret or not generally known
(2) (meaning too rare to warrant focus)
meaning too rare to warrant focus:

More rarely, privy can refer to a hidden place, outhouse, or toilet.