Synonyms for Unreasonable (same or very similar meaning)
WordNet sense 1 (lacking justification or authorization):
undue, unjustified, unwarrantedWordNet sense 2 (not marked by the use of reason):
senselessWordNet sense 3 (beyond normal limits):
excessive, inordinateWordNet sense 4 (not within reasonable limits):
immoderateFrom the ODE community, based on WordNetadd/edit