The Collaborative International Dictionary of English v.0.48:

dressed-up \dressed-up\ adj.
   attired in fancy or formal clothing. [Narrower terms:
   dressed to kill(predicate)]

   Syn: dressed to the nines(predicate), dolled up, spruced up,
        spiffed up.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

dressed-up
    adj 1: dressed in fancy or formal clothing [syn: dressed(p),
           dressed-up, dressed to the nines(p), dressed to
           kill(p), dolled up, spruced up, spiffed up,
           togged up]