Both of these adverbs are used in the AV of the English Bible (the KJV); however, one (privily) is erroneously being relegated to the archaic pile. We should understand these words before discarding!
Privily - About the knowledge of something secret. (As a spy would endeavor to discover).
Privately - Set apart (from the public). Made alone, unattached. ( A privateer is an armed vessel, owned by persons apart from public accountability).
Technically, an Army private is actually unranked, he is a private – unattached. (However, presently a Private is considered to hold the lowest rank).
And, the Privy Council not only meets in a separate situation from the public, they meet for the purpose of pursuing or acting on secret information. Most kings (Including King James) had a privy council - close advisors sharing discreet information.
Now with that in mind, look how the text of the Bible comes alive! [My comments]
“Then Joseph her husband, being a just man, and not willing to make her a publick example [wished to keep this matter private], was minded to put her away privily [act on the secret information: Mary was pregnant!] “ - Matthew 1:19.
See the two adverbs, related but definitely different, in use?
And another example:
“Then Herod, when he had privily called the wise men, inquired of them diligently what time the star appeared” - Matthew 2:7.
Note the emphasis of this text is on getting information - diligently, and not so much being apart from public view. Privily is the correct adverb.
And another:
“…I preach among the Gentiles, but privately to them which were of reputation…”
- Gal. 2:6.
(Which class of people was Paul dealing with? We know he separated them – apart. Privately is correct).
And, in the very next sentence:
“…false brethren unawares [in secret] brought in, who came in privily to spy…” - Gal 2:4.
(They were secretly seeking information, as a spy does - privily is correct).
One more:
“…he departed thence by a ship into a desert place apart…” - Matthew 14:13
In this text Jesus separates from the public (temporarily). It’s great the KJV, for clarity, includes the word “apart.” Which adverb, privily or privately, would be used to describe this action?
Of course, the Bible is it’s own best dictionary:
“And they departed into a desert place [not a public place] by ship privately.” Mark 6:32
Here the location, relative to the public, is emphasized – privately is correct.
Cool beans. Accuracy, and descriptive clarity. Let’s learn about these exact tools of language before they are relegated as archaic, and subsequently jettisoned from our toolbox.