First sergeant and Sergeant

First sergeant noun - A sergeant in the Army above the rank of staff sergeant and below master sergeant.

Sergeant and first sergeant are semantically related. In some cases you can use "Sergeant" instead a noun phrase "First sergeant".

Sergeant noun - Any of several noncommissioned officer ranks in the Army or Air Force or Marines ranking above a corporal.

First sergeant and sergeant are semantically related. Sometimes you can replace phrase "First sergeant" with "Sergeant", this terms are similar.