rational

UK: /ˈræʃ^ənəl/ US: /ˈræʃənəl, ˈræʃnəl/ ,(rash′ə nl, rash′nl)

WordReference Random House Learner's Dictionary of American English © 2026

ra•tion•al /ˈræʃənəl, ˈræʃnəl/   adj. 

1. based on reason; fitting in with reason;
   sensible:
   a rational decision.
2. using reason:
   a rational negotiator.
3. sane;
   able to think or speak clearly and logically:
   The patient seems perfectly rational.

ra•tion•al•i•ty /ˌræʃəˈnælɪti/  n. [uncountable]
ra•tion•al•ly, adv. See -ratio-.

WordReference Random House Unabridged Dictionary of American English © 2026

ra•tion•al  (rash′ə nl, rash′nl), adj. 

1. agreeable to reason;
   reasonable;
   sensible:
   a rational plan for economic development.
2. having or exercising reason, sound judgment, or good sense:
   a calm and rational negotiator.
3. being in or characterized by full possession of one's reason;
   sane;
   lucid:
   The patient appeared perfectly rational.
4. endowed with the faculty of reason:
   rational beings.
5. of, pertaining to, or constituting reasoning powers:
   the rational faculty.
6. proceeding or derived from reason or based on reasoning:
   a rational explanation.
7. Mathematics
   • capable of being expressed exactly by a ratio of two integers.
   • (of a function) capable of being expressed exactly by a ratio of two polynomials.
8. Poetry [Class. Pros.] capable of measurement in terms of the metrical unit or mora.

n. 

9. [Math.] See rational number. 

• Latin ratiōnālis, equivalent. to ratiōn- (stem of ratiō) reason + -ālis -al¹
• Middle English racional 1350–1400

ra′tion•al•ly, adv. 
ra′tion•al•ness, n. 
Synonyms

• 2. intelligent, wise, judicious, sagacious, enlightened.
• 6. See reasonable. 

Antonyms

• 2. stupid.
• 3. insane.

Collins Concise English Dictionary © HarperCollins Publishers::

rational / ˈræʃən^əl/ adjective

1. using reason or logic in thinking out a problem
2. in accordance with the principles of logic or reason; reasonable
3. of sound mind; sane: the patient seemed quite rational
4. endowed with the capacity to reason; capable of logical thought: humans are rational beings
5. expressible as a ratio of two integers or polynomials

noun

1. a rational number

Etymology: 14th Century: from Latin ratiōnālis, from ratiō reason

ˈrationally adverb

ˈrationalness noun