Pronunciation: (i-rash'u-nl),[key] —adj. 1. without the faculty of reason; deprived of reason.
2. without or deprived of normal mental clarity or sound judgment.
3. not in accordance with reason; utterly illogical: irrational arguments. 4. not endowed with the faculty of reason: irrational animals. 5. Math. a. (of a number) not capable of being expressed exactly as a ratio of two integers.
b. (of a function) not capable of being expressed exactly as a ratio of two polynomials.
6. Algebra.(of an equation) having an unknown under a radical sign or, alternately, with a fractional exponent.
7. Gk. and Lat. Pros. a. of or pertaining to a substitution in the normal metrical pattern, esp. a long syllable for a short one.
b. noting a foot or meter containing such a substitution.