active duty
1. Current, full-time service in the military. My son is in the army, and I worry so much when he's on active duty.
2. By extension, full-time service in another area of life. I'm still on active duty until I retire at the end of the month.
active duty
Full-time service, as in Julian is 81, but he still comes to the office every day and is very much on active duty . This term comes from the military, where it stands in opposition to reserve, which refers to troops still in the military but not actively engaged. It is occasionally transferred to civilian matters as well. [First half of 1800s]