[ rash-uh-nl, rash-nl ]
/ ˈræʃ ə nl, ˈræʃ nl /



Mathematics. rational number.

Origin of rational

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

Related forms

Can be confused

rational reasonable (see synonym study at reasonable)
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Examples from the Web for rational

British Dictionary definitions for rational


/ (ˈræʃənəl) /


using reason or logic in thinking out a problem
in accordance with the principles of logic or reason; reasonable
of sound mind; sanethe patient seemed quite rational
endowed with the capacity to reason; capable of logical thoughtman is a rational being
maths expressible as a ratio of two integers or polynomialsa rational number; a rational function


maths a rational number

Derived Forms

rationally, adverbrationalness, noun

Word Origin for rational

C14: from Latin ratiōnālis, from ratiō reason
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Medicine definitions for rational


[ răshə-nəl ]


Having or exercising the ability to reason.
Influenced by reasoning rather than by emotion.
Of sound mind; sane.
Based on scientific knowledge or theory rather than practical observation.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.