not reasonable or rational; acting at variance with or contrary to reason; not guided by reason or sound judgment; irrational

an unreasonable person.

not in accordance with practical realities, as attitude or behavior; inappropriate

His Bohemianism was an unreasonable way of life for one so rich.

excessive, immoderate, or exorbitant; unconscionable

an unreasonable price; unreasonable demands.

not having the faculty of reason.

noun

illogicality , illogicalness , irrationality