We don't have synonyms for seat-belt yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are seat belt, seatbelt and sea-beat.
(n) :
Alternative spelling of seat belt. [(automotive) A restraining belt attached to a vehicle seat and fastened around occupants in order to keep them in place and decelerate them smoothly rather than suddenly in an accident, mitigating the risk of injury from uncontrolled impact with injurious objects.]
(n) :
Alternative spelling of seat belt. [(automotive) A restraining belt attached to a vehicle seat and fastened around occupants in order to keep them in place and decelerate them smoothly rather than suddenly in an accident, mitigating the risk of injury from uncontrolled impact with injurious objects.]