Source : Webster's Revised Unabridged Dictionary (1913)

Unbecoming \Un`be*com"ing\, a. [Pref. un- not + becoming.]
   Not becoming; unsuitable; unfit; indecorous; improper.

         My grief lets unbecoming speeches fall.  --Dryden.
   -- {Un`be*com"ing*ly}, adv. -- {Un`be*com"ing*ness}, n.

Source : WordNet®

unbecomingness
     n : the quality of being unbecoming [ant: {becomingness}]