Learner's definition of DUTY
1 : something that is done as part of a job
His primary/main duty at the event is to take attendance.
If new employees are unable to carry out their duties, they may be fired.
She has a variety of administrative duties.
Please report for duty [=show up for work] at 7 a.m.
This year no firefighters/police were killed in the line of duty. [=while they were doing their jobs]
In helping them, he went beyond the call of duty. [=did more than he was required or expected to do]
2 : something that you must do because it is morally right or because the law requires it
They helped her out of a sense of duty.
I'll be ready when duty calls.
He was selected for jury duty. [=to serve on a jury]
3 [noncount] : active military service
Her brother returned from duty overseas.
a twelve-month tour of duty
Many reserve troops were called into active duty.
4 : a tax on goods that are being brought into a country
do duty as
1 : to do the work of (someone or something) 2 : to be used as (something)
: not working at a particular time
: working at a particular time