Chewing the fat, all finally understand (3)
I believe the answer is:
get
'understand' is the definition.
(I know that get is a type of understand)
'chewing the fat all finally' is the wordplay.
'all finally' indicates one should take the final letters.
The final letters of 'chewing the fat' are 'GET'.
(Other definitions for get that I've seen before include "Understand" , "Fetch or obtain" , "Receive; obtain" , "Procure from vegetables" , "Acquire" .)