redemptioner (n.)

mid-14c., redemcioun, "deliverance from sin," from Old French redemcion (12c.) and directly from Latin redemptionem (nominative redemptio) "a buying back or off, a releasing, a ransoming" (also "bribery"), noun of action from past-participle stem of redimere "to redeem, buy back," from red- "back" (see re-) + emere "to take, buy, gain, procure" (from PIE root *em- "to take, distribute").

The -d- is from the Old Latin habit of using red- as the form of re- before vowels, as also preserved in redact, redolent, redundant. The general sense of "release, repurchase, deliverance" is from late 15c. Commercial sense is from late 15c. Year of Redemption as "Anno Domini" is from 1510s. In the Mercian hymns, Latin redemptionem is glossed by Old English alesnisse.

English agent noun ending, corresponding to Latin -or. In native words it represents Old English -ere (Old Northumbrian also -are) "man who has to do with," from Proto-Germanic *-ari (cognates: German -er, Swedish -are, Danish -ere), from Proto-Germanic *-arjoz. Some believe this root is identical with, and perhaps a borrowing of, Latin -arius (see -ary).

Generally used with native Germanic words. In words of Latin origin, verbs derived from past participle stems of Latin ones (including most verbs in -ate) usually take the Latin ending -or, as do Latin verbs that passed through French (such as governor); but there are many exceptions (eraser, laborer, promoter, deserter; sailor, bachelor), some of which were conformed from Latin to English in late Middle English.

The use of -or and -ee in legal language (such as lessor/lessee) to distinguish actors and recipients of action has given the -or ending a tinge of professionalism, and this makes it useful in doubling words that have a professional and a non-professional sense (such as advisor/adviser, conductor/conducter, incubator/incubater, elevator/elevater).