[sergeant major] n, pl sergeants major or sergeant majors (1802) 1: a noncommissioned officer in the army, air force, or marine corps serving as chief administrative assistant in a headquarters
2: a noncommissioned officer in the marine corps ranking above a first sergeant
3: a bluish green to yellow bony fish (Abudefduf saxatilis of the family Pomacentridae) with black vertical stripes on the sides that is widely distributed in the western tropical Atlantic Ocean