1640s, "vindicatory, containing a defense," from French apologétique, from Latin apologeticus, from Greek apologetikos "defensible," from apologeisthai "speak in one's defense," from apologos "an account, story," from apo "away from, off" (see apo-) + logos "speech," from PIE root *leg- (1) "to collect, gather," with derivatives meaning "to speak (to 'pick out words')." Meaning "regretfully acknowledging failure" is from 1855.
