- Not endowed with reason. (adjective)
- Affected by loss of usual or normal mental clarity; incoherent, as from shock. (adjective)
- Marked by a lack of accord with reason or sound judgment: an irrational dislike. (adjective)
- Being a syllable in Greek and Latin prosody whose length does not fit the metric pattern. (adjective)
- Being a metric foot containing such a syllable. (adjective)
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.