Wiktionary
sergeant first class
n. (context US Army English) A non-commissioned officer in the United States Army, ranking above a staff sergeant and below a master sergeant or first sergeant.
WordNet
sergeant first class
n. a sergeant in the army above the rank of staff sergeant and below master sergeant [syn: first sergeant]
Wikipedia
Sergeant first class
Sergeant First Class is a military rank in some militaries and other uniformed organizations around the world, typically that of a senior non-commissioned officer.