Military rank in the army or air force, equivalent to sergeant. Used in both historical and modern contexts.
He was promoted to sergeant.
The sergeant commanded the unit.
He was promoted to sergeant after two years.
軍曹 is the army rank of sergeant, while 伍長 is one rank lower, equivalent to corporal.
From 軍 (army) and 曹 (official, rank). The exact historical derivation is uncertain, but the compound has been used for the sergeant rank in modern Japanese military terminology.