A Royal Navy officer holding the full rank of captain, as opposed to a commander with the courtesy title of captain.
〈史〉（皇家海军的）大舰长
Example sentencesExamples
He had made post captain when he was only twenty-three years old, not an unheard of feet, but he had been young enough to be hailed as one of the most promising officers in the King's service.
I can't resist pointing out that a master and commander would never captain a frigate, and quite properly the film has Aubrey wearing the two epaulettes of a post captain.