Douglas Harper's Etymology Dictionary
1747, short for non-commissioned officer.
Wiktionary
n. (context colloquial English) A non-commissioned officer.
Usage examples of "non-com".
Zim had tried out all of the older men as temporary non-coms first and I had inherited a brassard with chevrons on it a couple of days before when our squad leader had folded up and gone to hospital.
Behind the counter of the kitchen the non-coms, the jovial first sergeant, and the business-like sergeant who looked like a preacher, and the wrinkled-faced corporal who had been on the Red Sox outfield, could be seen eating steak.
Food was brought and Parkwood started a group of non-coms organizing replacements and duty rotations.
It was ingrained in them all, from the rawest recruit to the most senior non-com: hypnotically drilled into their brains.