master sergeant

Short definition from Wiktionary

Noun

1. 1
   A non-commissioned officer in the United States Army, ranking above sergeant first class and below sergeant major; equal in grade and pay to a first sergeant.
2. 2
   A non-commissioned officer in the United States Marine Corps, ranking above gunnery sergeant and below master gunnery sergeant or sergeant major.
3. 3
   A non-commissioned officer in the United States Air Force, ranking above technical sergeant and below senior master sergeant.