A person of authority in the military who has not received a commission (a direct conveyance of authority from the sovereign government); as such they can have charge or control but not command in the most technical use of the word
A platoon sergeant may only be a non-commissioned officer but he's the one his men look to when the bullets start flying.
non-commissioned in AM, use noncommissioned A non-commissioned officer in the armed forces is someone with a rank such as corporal or sergeant who used to have a lower rank, rather than an officer of higher rank who has been given a commission