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