ra·tion·alˈraSH(ə)n(ə)l/adjective1.based on or in accordance with reason or logic."I'm sure there's a perfectly rational explanation"synonyms:logical, reasoned, sensible, reasonable, cogent, intelligent, judicious, shrewd,common-sense, commonsensical, sound, prudent; More2.MATHEMATICS(of a number, quantity, or expression) expressible, or containing quantities that are expressible, as a ratio of whole numbers. When expressed as a decimal, a rational number has a finite or recurring expansion.nounMATHEMATICS1.a rational number.