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c.1300, "having sound judgment, sane, rational," from Old French raisonable, from Latin rationabilis, from ratio (see reason (n.)).
What the majority of people consider to be 'reasonable' is that about which there is agreement, if not among all, at least among a substantial number of people; 'reasonable' for most people, has nothing to do with reason, but with consensus. [Erich Fromm, "The Heart of Man," 1968]Meaning "moderate in price" is recorded from 1660s. Related: Reasonably.