rational

1 having the ability to reason human beings are rational creatures Synonyms intelligent, reasonable, reasoning, thinking Related Words analytic (or analytical), logical; brainy, cerebral, highbrow, highbrowed, intellectual; cognitional, cognitive, mental; levelheaded, practical, sane, sensible, sober Near Antonyms brainless, dense, doltish, dopey (also dopy), dorky [slang], dull, dumb, fatuous, half-witted, mindless, obtuse, senseless, slow, stupid, thickheaded; fallacious, groundless, illogical, invalid, nonsensical Antonyms irrational, nonrational, nonthinking, unintelligent, unreasonable, unreasoning, unthinking

2 according to the rules of logic insisted there was a rational explanation for the strange creaking noises and that there were no such things as ghosts Synonyms analytic (or analytical), coherent, consequent, good, logical, reasonable, sensible, sound, valid, well-founded, well-groundedRelated Words a posteriori, a priori, syllogistic; cognitive, empirical (also empiric); defendable, defensible, justifiable, maintainable, supportable, sustainable, tenableNear Antonyms casuistic (or casuistical), eristic (also eristical), fallacious, misleading, sophistic (or sophistical), specious; unarticulated; unscientific; absurd, cockeyed, crazy, daffy, fatuous, half-baked, half-witted, harebrained, insane, loony (also looney), mad, nonsensical, nutty, preposterous, simpleminded, stupid, weak-minded, witless; senseless, thoughtless; uncompelling, unconvincingAntonyms illegitimate, illogical, incoherent, inconsequent, inconsequential, invalid, irrational, unreasonable, unsound, weak

3 based on sound reasoning or information betting all of your savings on the lottery is not a rational move Synonyms commonsense, commonsensible, commonsensical, firm, hard, informed, just, justified, levelheaded, logical, good, reasonable, reasoned, sensible, sober, solid, valid, well-foundedRelated Words actual, real, true; certain, sure; certified, validated, verified; confirmed, corroborated, substantiated; cogent, convincing; colorable, credible, plausibleNear Antonyms unsubstantiated, unsupported, unwarranted; flimsy, implausible, unconvincing, weak; fallacious, false, misguided, misledAntonyms groundless, illogical, invalid, irrational, nonrational, nonsensical, nonvalid, unfounded, uninformed, unjustified, unreasonable, unreasoned, unsound