adj. 1. Having or exercising the ability to reason. See Synonyms at logical. 2. Consistent with or based on reason or good judgment; logical or sensible: rational decisions. 3. Of sound mind; sane: wondered if the eccentric neighbor was not completely rational. 4. Mathematics Capable of being expressed as a quotient of integers. n. Mathematics A rational number. [Middle English racional, from Old French racionel, from Latin ratiōnālis, from ratiō, ratiōn-, reason; see REASON.] ration·al·ly adv. ration·al·ness n. |
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