The Collaborative International Dictionary of English v.0.48:

Housewarming \House"warm`ing\, n.
   A feast or merry-making made by or for a family or business
   firm on taking possession of a new house or premises.
   --Johnson.
   [1913 Webster]

WordNet (r) 3.0 (2006):

housewarming
    n 1: a party of people assembled to celebrate moving into a new
         home

Moby Thesaurus II by Grady Ward, 1.0:

72 Moby Thesaurus words for "housewarming":
   Kaffeeklatsch, assemblee, assembly, assignation, at home, ball,
   blowout, brawl, caucus, cocktail party, coffee klatch, colloquium,
   commission, committee, conclave, concourse, congregation, congress,
   conventicle, convention, convocation, costume party, council,
   dance, date, diet, dinner, dinner party, donation party,
   eisteddfod, entertainment, festivity, fete, forgathering, forum,
   garden party, gathering, get-together, hen party, house party,
   house-raising, lawn party, levee, mask, masque, masquerade,
   masquerade party, meet, meeting, panel, party, plenum, prom,
   quorum, rally, reception, rendezvous, seance, session, shindig,
   shindy, shower, sit-in, sitting, smoker, soiree, stag, stag party,
   surprise party, symposium, synod, turnout