The Collaborative International Dictionary of English v.0.48:

Lifeboat \Life"boat`\ (l[imac]f"b[=o]t`), n.
   A strong, buoyant boat especially designed for saving the
   lives of shipwrecked people.
   [1913 Webster]

WordNet (r) 3.0 (2006):

lifeboat
    n 1: a strong sea boat designed to rescue people from a sinking
         ship

Moby Thesaurus II by Grady Ward, 1.0:

33 Moby Thesaurus words for "lifeboat":
   Mae West, air-sea rescue, bolt-hole, breeches buoy, buoy,
   coast guard, cork jacket, ejection capsule, ejection seat,
   ejector seat, emergency exit, escape hatch, fire escape,
   inflatable slide, life belt, life buoy, life jacket, life net,
   life preserver, life raft, life ring, life vest, lifeguard,
   lifeline, lifesaver, parachute, rescuer, rubber dinghy,
   safety belt, sally port, savior, slide, water wings