early 15c., "defense, justification," from Late Latin apologia, from Greek apologia "a speech in defense," from apologeisthai "to speak in one's defense," from apologos "an account, story," from apo "away from, off" (see apo-) + logos "speech" (see Logos).
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.