Able Bodied Seamen (A.B.)
Some modern references claim that AB stands for able-bodied seaman as well as, or instead of, able seaman. Able seaman was originally entered using the abbreviation AB instead of the more obvious AS in ships' muster books or articles. Such an entry was likely to avoid confusion with ordinary seaman (OS). Later the abbreviation began to be written as A.B., leading to the folk-etymological able-bodied seaman. The correct term, able seaman, remains in use in legal documents, in seaman's papers, and aboard ship.