WordNet (r) 3.0 (2006):

seat belt
    n 1: a safety belt used in a car or plane to hold you in your
         seat in case of an accident [syn: seat belt, seatbelt]

Moby Thesaurus II by Grady Ward, 1.0:

61 Moby Thesaurus words for "seat belt":
   aegis, arm guard, backstop, buffer, bulwark, bumper, contraceptive,
   copyright, crash helmet, cushion, dashboard, dodger, face mask,
   fender, finger guard, foot guard, fuse, goggles, governor, guard,
   guardrail, hand guard, handrail, hard hat, helmet, insulation,
   interlock, knee guard, knuckle guard, laminated glass,
   life preserver, lifeline, lightning conductor, lightning rod, mask,
   mudguard, nose guard, pad, padding, palladium, patent, pilot,
   preventive, prophylactic, protective clothing, protective umbrella,
   safeguard, safety, safety glass, safety plug, safety rail,
   safety shoes, safety switch, safety valve, screen, shield,
   shin guard, sun helmet, umbrella, windscreen, windshield