Learn That Word

Synonyms for Unreasonable (same or very similar meaning)

WordNet sense 1 (lacking justification or authorization):
undue, unjustified, unwarranted

WordNet sense 2 (not marked by the use of reason):

WordNet sense 3 (beyond normal limits):
excessive, inordinate

WordNet sense 4 (not within reasonable limits):

From the ODE community, based on WordNetadd/edit