an officer, acting under the officer of the day, who is responsible for the instruction, discipline, and performance of duty of the guard in a post, camp, or station.
Abbreviation: OG, O.G.
Examples from the web for officer of the guard
The two ex-rulers were not allowed to meet or converse together, even at meals, without an officer of the guard at their elbow.
British Dictionary definitions for officer of the guard
officer of the guard
noun
1.
a junior officer whose duty is to command a ceremonial guard OG