Outer form of path (5)
I believe the answer is:
route
'path' is the definition.
(I know that path can be written as route)
'outer form' is the wordplay.
'form' is an anagram indicator (another form of the letters).
'outer' anagrammed gives 'ROUTE'.
'of' is the link.
(Other definitions for route that I've seen before include "Course to destination" , "Path taken" , "Course followed" , "Course, road" , "Choice of roads in an itinerary" .)