relating to the reason; not physical; mental.-having reason, or the faculty of reasoning; endowed with reason or understanding; reasoning.-agreeable to reason; not absurd, preposterous, extravagant, foolish, fanciful, or the like; wise; judicious; as, rational conduct; a rational man.-expressing the type, structure, relations, and reactions of a compound; graphic; -- said of formulae. see under formula.-a rational being.