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):

unbecomingly
    adv 1: without decorousness [syn: indecorously,
           unbecomingly] [ant: decorously]