an officer in command of a military unit
WordReference Random House Unabridged Dictionary of American English © 2025
command′ing of′ficer,
- [Army.]a commander of any rank from second lieutenant to colonel.
- 1790–1800
Collins Concise English Dictionary © HarperCollins Publishers::
'commanding officer' also found in these entries (note: many are not synonyms or translations):
CO
- adjutant
- cabin
- commandant
- commanding
- general headquarters
- mister
- old man
- order of the day
- orderly
- responsible
- staff
- wardroom