Source : Webster's Revised Unabridged Dictionary (1913)

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.

Source : WordNet®

unwarrantably
     adv : in an unwarrantable manner or to an unwarranted degree; "in
           this painting, the relationship of the upper part of
           the body to the lower is uneasy and the right thigh
           seems unwarrantably stressed"