The Collaborative International Dictionary of English v.0.48:

break-in \break-in\ n.
   an act of trespassing into a closed structure such as a house
   or place of busineess for an unlawful purpose, usually as
   part of a burglary.

   Syn: housebreaking, breaking and entering.
        [WordNet 1.5 +PJC]

WordNet (r) 3.0 (2006):

break-in
    n 1: trespassing for an unlawful purpose; illegal entrance into
         premises with criminal intent [syn: housebreaking,
         break-in, breaking and entering]