The Collaborative International Dictionary of English v.0.48:
Unwarrantable \Un*war"rant*a*ble\, a. Not warrantable; indefensible; not vindicable; not justifiable; illegal; unjust; improper. -- Un*war"rant*a*ble*ness, n. -- Un*war"rant*a*bly, adv. [1913 Webster]