In classical Greek, "a well-reasoned reply; a 'thought-out response' to the accusations made," as that of Socrates. The original English sense of "self-justification" yielded a meaning "frank expression of regret for wrong done," first recorded 1590s, but this was not the main sense until 18c. Johnson's dictionary defines it as "Defence; excuse," and adds, "Apology generally signifies rather excuse than vindication, and tends rather to extenuate the fault, than prove innocence," which might indicate the path of the sense shift. The old sense has tended to shift to the Latin form apologia (1784), known from early Christian writings in defense of the faith.
"defense, justification," 1784, the Latin form of apology (q.v.); popularized by J.H. Newman's "Apologia pro Vita Sua" (1864). It preserves the older sense of the English apology and the sense of the Greek original, especially as used by the Church fathers.
In common Greek, apologia refers to the speech that an accused person delivered in court, rejecting the charges filed against him or her. The apologists of the second century chose this term because they wanted to show that the charges filed against Christians were unjustified and that the truths of their faith could be described and defended. An apologia was dedicated to the Roman empoeror, who certainly never read it. [Max L. Stackhouse, "Apologia," 1988]
"making excuse; containing an excuse or apology, apologetical," mid-15c., from Old French excusatoire, from Medieval Latin excusatorius, from Latin excusare "excuse, make an excuse for" (see excuse (v.)).
mid-15c., pardounen, "to forgive for offense or sin," from Old French pardoner and Medieval Latin perdonare (see pardon (n.)).
'I grant you pardon,' said Louis XV to Charolais, who, to divert himself, had just killed a man; 'but I also pardon whoever will kill you.' [Marquis de Sade, "Philosophy in the Bedroom"]
Related: Pardoned; pardoning. Pardon me as a phrase used when making apology is by 1764; pardon my French as exclamation of apology for obscene language is by 1895.
"with the leave of, by the permission of," 1863, from Latin pace, ablative of pax "peace," as in pace tua "with all deference to you;" from PIE root *pag- "to fasten." "Used chiefly as a courteous or ironical apology for a contradiction or difference of opinion" [OED]. It is sometimes misused as though it means "according to" instead of the opposite.
"make mention of, speak of briefly or cursorily," 1520s, from mention (n.) or else from French mentionner, from Old French mencion. Related: Mentioned; mentioning. Not to mention as a "rhetorical suggestion that the speaker is refraining from presenting the full strength of his case" [OED] is by 1690s. Don't mention it as a conventional reply to expressions of gratitude or apology is attested from 1840.
late 14c., purgacioun, "purification from sin," also "discharge of waste; evacuation of evil humors by bloodletting, etc.," from Old French purgacion "a cleansing," medical or spiritual (12c., Modern French purgation) and directly from Latin purgationem (nominative purgatio) "a cleansing, purging," figuratively "an apology, justification," noun of action from past-participle stem of purgare "to cleanse, purify" (see purge (v.)).