- Having or exercising the ability to reason. (adjective)
- Of sound mind; sane. (adjective)
- Consistent with or based on reason; logical: rational behavior. See Synonyms at logical. (adjective)
- Mathematics Capable of being expressed as a quotient of integers. (adjective)
- Mathematics A rational number. (noun)
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.