Duty/ˈduːti/ Definition 1 of 4Pro Tip 1/3Job Requirement Refer to responsibilities that must be completed during work hours or as part of a role. As a firefighter, saving lives is his primary duty. Pro Tip 2/3Obligatory Task Emphasizes an action expected by society, not chosen personally. Jury service is a civic duty. Pro Tip 3/3Professional Context Use 'on duty' to indicate someone is currently working their job. The nurse on duty took care of the patients throughout the night.