irrational

Irrational is defined as lacking reason or understanding.

(adjective)

An example of irrational is a fear of a certain color.

The definition of an irrational is a number that cannot be expressed as a fraction.

(noun)

An example of irrational is pi.

See irrational in Webster's New World College Dictionary

adjective

lacking the power to reason
contrary to reason; senseless; unreasonable; absurd
Math. designating a real number not expressible as an integer or as a quotient of two integers: √ and pi are irrational numbers

Origin: ME < L irrationalis: see in- & rational

Related Forms:

See irrational in American Heritage Dictionary 4

adjective

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