Definitions for "Petty Officer"
a noncommissioned officer in the navy with a rank comparable to sergeant in the army
Rank intermediate between officer and rating, and in charge of ratings. Usually messed apart from ratings, and has special privileges appropriate to his position.
a crew member who ranks between officer and rating, and is in charge of the ratings
Included gunner's mates, quartermasters, master-at-arms, carpenter, bosun and cooper, the ship's master, chaplain and surgeon