A case for partnership — part of joint strategy (8)
I believe the answer is:
approach
'strategy' is the definition.
(thesaurus)
'a case for partnership part of joint' is the wordplay.
'case for' means to remove the middle letters (the letters which encase the others are used).
'part of joint' becomes 'roach' (I can't justify this - if you can you should believe this answer much more).
'partnership' with its centre removed is 'pp'.
'a'+'pp'+'roach'='APPROACH'
Can you help me to learn more?
(Other definitions for approach that I've seen before include "Draw near or nearer to" , "initial proposal" , "Go towards" , "Advance towards" , "technique" .)