Course provided by alternative practitioner leaving base close to Oslo (4)
I believe the answer is:
path
'course' is the definition.
(synonyms)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for path that I've seen before include "Trodden track" , "Course of action; track" , "Route, course" , "Way for pedestrians" , "Will's go" .)