- do one's duty
- do one's duty1. to do one's job; to do what is expected of one. •
Please don't thank me. I'm just doing my duty.
•Soldiers who fight in wars are doing their duty.
2. Euph. to defecate or urinate. •We're not leaving this restroom until you do your duty.
•She did her duty in the potty, just like a big girl!
Dictionary of American idioms. 2013.