Staff sergeant and Sergeant first class

Staff sergeant noun - A noncommissioned officer ranking above corporal and below sergeant first class in the Army or Marines or above airman 1st class in the Air Force.

Sergeant first class and staff sergeant are semantically related. In some cases you can replace phrase "Sergeant first class" with "Staff sergeant", this phrases are similar.

Sergeant first class noun - A sergeant in the Army above the rank of staff sergeant and below master sergeant.

Staff sergeant and sergeant first class are semantically related. Sometimes you can replace phrase "Staff sergeant" with "Sergeant first class", this phrases are similar.