rational

 
Pronunciation: /ˈraʃ(ə)n(ə)l/

adjective

  • 1based on or in accordance with reason or logic: I’m sure there’s a perfectly rational explanation
  • able to think sensibly or logically: Ursula’s upset—she’s not being very rational
  • endowed with the capacity to reason: man is a rational being
  • 2 Mathematics (of a number, quantity, or expression) expressible, or containing quantities which are expressible, as a ratio of whole numbers.

Derivatives

rationality

Pronunciation: /-ˈnalɪti/
noun

rationally

adverb

Origin:

late Middle English (in the sense 'having the ability to reason'): from Latin rationalis, from ratio(n-) 'reckoning, reason' (see ratio)