Altered outer course (5)
I believe the answer is:
route
'course' is the definition.
(I've seen this before)
'altered outer' is the wordplay.
'altered' is an anagram indicator.
'outer' anagrammed gives 'ROUTE'.
(Other definitions for route that I've seen before include "Course taken" , "Course followed" , "Choice of roads in an itinerary" , "Course, path" , "Established line of trave" .)