Mission, task (6)
I believe the answer is:
errand
I believe this clue is a double definition.
'mission' is the first definition.
(I've seen this before)
'task' is the second definition.
(an errand is a task or job)
(Other definitions for errand that I've seen before include "Messenger's job" , "Gone up" , "Trip for small task" , "Journey to deliver message etc" , "An ...... of mercy is a journey to relieve distress" .)