Shrewd in the old way (4)
I believe the answer is:
wise
I believe this clue is a double definition.
'shrewd' is the first definition.
(thesaurus)
'the old way' is the second definition.
(I've seen this before)
'in' is the link.
(Other definitions for wise that I've seen before include "Old and knowledgable" , "Astute" , "Having discernment" , "comedian" , "Judicious" .)