Outer deviation in course (5)
I believe the answer is:
route
'course' is the definition.
(I've seen this before)
'outer deviation' is the wordplay.
'deviation' indicates an anagram.
'outer' is an anagram of 'ROUTE'.
'in' acts as a link.
(Other definitions for route that I've seen before include "Way, line" , "Established line of trave" , "Course of 7" , "Way to travel" , "Course taken" .)