Fool and knave see eye to eye (6)
I believe the answer is:
'see eye to eye' is the definition.
(I've seen this in another clue)
'fool and knave' is the wordplay.
'fool' becomes 'con' (I've seen this in another clue).
'and' says to put letters next to each other.
'knave' becomes 'cur' (I've seen this in another clue).
(Other definitions for concur that I've seen before include "Give assent" , "Agree or happen together" , "share the same opinion" , "Agree, assent" , "Stone pile" .)