on, on duty, on-duty - performing or scheduled for duties; "I'm on from five to midnight"; "Naval personnel on duty in Alaska"; "her on-duty hours were 11p.m. to 7 a.m." Antonym:inactive (indirect, via active)
Adverbialon has 3 senses
along, on - with a forward motion; "we drove along admiring the view"; "the horse trotted along at a steady pace"; "the circus traveled on to the next city"; "move along"; "march on"