Unreasonable
Part of speech: adjective
Definition: not reasonable
Example sentence: A monomaniac is a sick person whose mentality is perfectly healthy in all respects but one; he has a single flaw, clearly localized. At times, for example, he has an unreasonable and absurd desire to drink or steal or use abusive language; but all his other acts and all his other thoughts are strictly correct.
Untenable
Part of speech: adjective
Definition: Not able to be held, as of an opinion or position; unholdable, indefensible.