A synonym for unfrock, which is, according to Webster 1913,
"to deprive or divest or [sic]1 a frock; specifically, to deprive of priestly character or privilege; as, to unfrock a priest."
Why our good friend Webster 1913 was unaware of this, I do not know, because clearly the preferred term is "defrock", rather than "unfrock".
How do I know this, you ask?
Simple. I asked the Tool Of Objective Truth.
And it told me, "word count: unfrock: 85; defrock: 411"
1 I think "of" is the correct word here...