WordNet (r) 3.0 (2006):

life jacket
    n 1: life preserver consisting of a sleeveless jacket of buoyant
         or inflatable design [syn: life jacket, life vest,
         cork jacket]

Moby Thesaurus II by Grady Ward, 1.0:

20 Moby Thesaurus words for "life jacket":
   Mae West, breeches buoy, buoy, cork jacket, ejection capsule,
   ejection seat, ejector seat, life belt, life buoy, life net,
   life preserver, life raft, life ring, life vest, lifeboat,
   lifeline, parachute, rubber dinghy, safety belt, water wings