Synonyms for Unreasonable:

adj.

absurd (adjective)
goofy.
expensive (adjective)
inflated, rich, dear, overpriced, premium, overboard, costly, expensive, uneconomical, outrageous, extravagant, exorbitant, invaluable, Oversold, priceless, high-priced.
extravagant; beyond normal limits (adjective)
inordinate, excessive, undue, unwarranted, unjust, immoderate, unfair, dear, unconscionable, extreme, wrongful, exorbitant.
extreme (adjective)
extreme.
foolish (adjective)
cockamamy, zany.
not logical or sensible (adjective)
reasonless, arbitrary, silly, wrong, vacant, illogical, thoughtless, absurd, senseless, foolish, Unreasoned, biased.
thoughtless (adjective)
unthinking, mindless, unthoughtful, fatuous, thoughtless, illogical, blank, brainless, vacuous, vacant, empty-headed, inane, unoccupied.
unjust (adjective)
unfair.
unwarranted (adjective)
unwarranted.

n.

perverse, wrong, hysterical, irresponsible, childish. Unreasoned, reason. unconscionable, obscene, usual, shocking. illogical (noun)
biased.
immoderate (noun)
extreme.
unfair (noun)
partial, arbitrary, unjust, one-sided, unequal, unfair, wrongful.
unreasonable (noun)
foolish, excessive, illogical, silly, cockamamy, cockamamie, absurd, reasonless, unjustified, fool, mindless, zany, unlogical, unrealistic, goofy, inordinate, unwarranted, whacky, counterintuitive, senseless, undue, immoderate, untenable, sappy, wacky, indefensible.

Other synonyms:

wrong, Unreasoned, childish, irresponsible, arbitrary. hysterical, perverse, extreme. obscene. shocking. excessive
unconscionable, excessive.
unfair
unequal, biased, unjust, one-sided.
unrealistic
unrealistic.
Other relevant words:
obscene, unwarranted, excessive, silly, unjustified, fool, foolish, senseless, sappy, untenable, one-sided, counterintuitive, unjust, irresponsible, unequal, undue, arbitrary, extreme, unconscionable, unrealistic, shocking, immoderate, childish, unlogical, indefensible, biased, cockamamie, reasonless, perverse, wrong, unfair, whacky, inordinate, wrongful, Unreasoned, goofy, cockamamy, wacky, absurd, zany.

Usage examples for unreasonable

  1. If he had been like some of you, he would have said, " What an unreasonable command! – Godliness by Catherine Booth
  2. And, indeed, said Socrates, it would appear to be unreasonable yet still, perhaps, it has some reason on its side. – Apology, Crito, and Phaedo of Socrates by Plato
  3. Hang it all, Pancaldi, you're unreasonable – The Eight Strokes of the Clock by Maurice Le Blanc