on duty
WORKING, at work, busy, occupied, engaged, on the job, tied up

[TahlilGaran] Dictionary of Contemporary English ▲

on duty
working.
A physical therapist is on duty in the fitness center from 7 a.m. until 9 p.m.

He didn't have time to talk about it right then because he was on duty for another three hours.

Usage notes: usually said about soldiers, police, medical workers, and people who work a scheduled period of time

[TahlilGaran] English Idioms Dictionary ▲

on duty
to be at work, to be currently doing one's work
There was nobody on duty when we arrived at the swimming pool.

[TahlilGaran] English Idioms Dictionary ▲

on duty
adj. phr. Doing one's job; supervising.
Two soldiers are on duty guarding the gates.
There is always one teacher on duty during study hour.
Antonym: OFF DUTY.

[TahlilGaran] English Idioms Dictionary ▲