person on duty; duty officer
Refers to a staff member assigned to be on duty, commonly used in hospitals, fire stations, and other workplaces with shift rotations.
The person on duty tonight is Mr. Yamada.
Please transfer the call to the duty officer.
Compound of 当直 (duty, being on duty) and 員 (member, person). The exact historical derivation is uncertain, but the word follows a common pattern for naming roles in institutional settings.