| 1. | U.S. Army, Air Force, and Marine Corps. a noncommissioned officer serving as chief administrative assistant in a unit headquarters. |
| 2. | U.S. Marine Corps. a noncommissioned officer ranking above a first sergeant. |
| 3. | a small damselfish, Abudefduf saxatilis, inhabiting warm Atlantic waters, having vertical black stripes on each side. |

| sergeant major n. pl. sergeants major or sergeant majors
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