The Collaborative International Dictionary of English v.0.48:
Unbecoming \Un`be*com"ing\, a. [Pref. un- not + becoming.] Not becoming; unsuitable; unfit; indecorous; improper. [1913 Webster] My grief lets unbecoming speeches fall. --Dryden. [1913 Webster] -- Un`be*com"ing*ly, adv. -- Un`be*com"ing*ness, n. [1913 Webster]WordNet (r) 3.0 (2006):
unbecomingness n 1: the quality of being unbecoming [ant: becomingness]