It looks like I struck out on a ‘definitive’ (pun intended) explication of ‘confessor.’
It seems that ‘confessor’ is used for both the one confessing, as in the normal use of the -or in English, and as the one, usually a priest, to whom confession is made. I discovered this Sunday evening when I was replying to a comment by Angel at my "Librarianship as Penance?" post. What, I asked, is up with that?
My initial foray for an answer is at my post, "Dictionary Day, now this is a holiday that I can get behind." Feel free to take a look, I’ll wait. I initially looked in the OED online to verify that it was used in both ways. I looked at etymologies, first uses (descriptive), and spellings. Unless I’m missing something in some Latin tense that isn’t fully explained, I don’t see why it is used both ways.
So Wednesday I hit the main reference room, the LIS Library, the Modern Languages Library, and then the History and Philosophy (Religion) Library.
But first, here is what I found in the main reference room. I began with verifying what I found in the online OED with the print version. I decided to check ‘confessee’ and discovered the following:
confessee rare. [f. CONFESS v. + -EE]
a. One who is confessed (by a priest). b. One to whom confession is made. (Ambiguous and to be avoided.)
[OK, do they mean these uses are ambiguous, or their definition is, or both?]
1601 F. GODWIN Bps. Eng. 377 Either the Confessor, or the Confessee, or the reporter, lied I doubt not. 1839 J. ROGERS Antipopopr. xiv. §1. 305 Confessor and confitent, or rather confessee and confesser commonly in private.
confesser [f. CONFESS v. + -ER] One who confesses or makes confession.
1836-46 in SMART Walker’s Dict. 1839 [see prec.].
[Again, kind of ambiguous.]
I then looked in:
Etymological Dictionary of the English Language, 3rd ed. Rev. Walter W. Skeat. Oxford : Clarendon Press, 1898
The Oxford Dictionary of English Etymology. C.T. Onions, ed. Oxford : Clarendon Press, 1966
Origins: a Short Etymological Dictionary of Modern English, 4th ed. Eric Partridge New York : Macmillan, 1966
confess, confession, confessional (adj., n), confessor.
‘To confess‘ derives, via OF-F, from LL confessāre, from L confess-, s of confessus, pp of confitēri, to confess,…
confessor, adopted by OF (whence the F confesseur), passes into E.
OF Old French / F French / LL Late Latin (c A.D. 180-600) / L Latin / s stem / pp past participle
Suffixes and Other Word-Final Elements of English Laurence Urdang, ed. Detroit, MI : Gale Research Company, 1982
1273 -or A noun-forming word-final element, derived through Middle English -or, -our and Old French -eor, -eur from the Latin agentive suffix -or, -ator, used to denote ‘a person or thing that performs and action’ specified by the combining root: councillor, sailor, elevator. Related forms: -ors (plural).
1274 -or A noun-forming word-final element, derived through Middle English -or, -our and Old French -eor, -eur from the Latin abstract-noun-forming suffix -or, used in combinations denoting ‘an action, state, condition, result, quality, or characteristic’ specified by the combining root: labor, candor, misdemeanor. Also, -our (British). Related forms: -ors (plural). [I don't think this applies here, but wanted to be inclusive.]
I also looked in several other "standard" unabridged dictionaries. None gave me any insight. So I headed off to the LIS Library to ask my friends their recommendations on which "experts" to go bug. I went on my merry way to the English Library but decided to bypass it based on staffing and headed to the Modern Languages Library. There I talked with a nice gentleman librarian with some sort of British Empire accent. We decided that I had tried all of the standard routes and that it is probably some combination of my two theses (I’m getting there!) or in other words, an accident of language. He suggested I go talk to the religious folks over in History and Philosophy so off I trundled. Luckily, all of these libraries are in the Main Library Building. A staffer there helped me but did much of the same sort of work I had already done, although I’m happy to let someone verify I’m not missing something obvious or even not so obvious. Again, we decided on some sort of sociological, accident of language answer.
This is not the answer I want. But seeing as it is human language, there may well be no "definitive" answer.
But before I give you my "answers," if anyone has any other ideas or, better yet, "the answer," please feel free to let me know. Also, if anyone can think of any other words in English that use the same word form of the -ee and -or family to designate the doer and recipient of an action, please let me know.
I am (currently) left with a sociological/accident of language answer, for which I have no real evidence. So, yes, I’m guessing.
The earliest sense in English per the OED, is "One who avows his religion in the face of danger, and adheres to it under persecution and torture, but does not suffer martyrdom; spec. one who has been recognized by the church in this character." The first recorded use of this sense, is c1000. This is also the first English usage. King Edward the Confessor fits this sense.
Then, (prior to) a1300 we get the first usage of the more general sense of "One who makes confession or public acknowledgement or avowal of anything" (OED).
And then in 1340 we get this use, "One who hears confessions: a priest who hears confession of sin, prescribes penance, and grants absolution; the private spiritual director of a king or other great personage" and this note, from the OED: [In med.L. better confessarius; but confessor in this sense is quoted by Du Cange from Walafrid Strabo (ob. 849).]
That note may be the one clue that I (or the others I consulted) am unable to interpret.
So my first idea is that both uses come from different word forms in Latin. The first use had a few hundred years to make its way from Latin to Late Latin to Old French and Middle English and get vernacularized from the more narrow technical meaning to the more general meaning. Then the Church decided to use another but related Latin word form, to which they were theoretically much closer as Latin scholars, which ended up as "the same word," or word form, in English and French. Accident of history.
My second idea is that the Church decided 300+ years later to use the same technical word to also refer to the one confessed to. The Church was still fairly strong in the 1300s and could well have imposed a 2nd use of the word on the faithful. Sociological explanation.
And that, my friends, is the best I’ve been able to come up with for now.