It's awfully rude to make a digression (6)
I believe the answer is:
detour
'a digression' is the definition.
(thesaurus)
'it's awfully rude to' is the wordplay.
'it's awfully' indicates anagramming the letters.
'rude'+'to'='rudeto'
'rudeto' is an anagram of 'DETOUR'.
'make' is the link.
(Other definitions for detour that I've seen before include "Circuitous alternative to direct path" , "Diversion" , "Way round the roadblock" , "Roundabout route, to avoid something say" , "Deviation from the usual route" .)