do duty—
1. serve as or pass for smth. else:
- The handsome building, could have done duty as a state capitol.
2. (euph.) defecate or urinate:
- The lamb stood in the middle of the field doing duties at an adjacent haystack.
do one’s duty—
1. do what one is obliged to do by law, one’s trade or conscience:
- “You’ve been very helpful, Aggie.” “I do my duty.”
2. = do duty 2:
- The child never defecates or urinates; he does his “duty.”
3. (euph.) is used of marital sex:
- Melinda could not stand the idea of the marriage bed and refused to do her duty as a wife.