Keenness more difficult for a Cockney, do we hear? (6)
I believe the answer is:
ardour
'keenness' is the definition.
(ardour is a kind of keenness)
'more difficult for a cockney do we hear?' is the wordplay.
'more difficult for a cockney' becomes 'arder' (Cockney pronunciation of 'harder').
'do we hear?' indicates a 'sounds like' (homophone) clue.
'arder' is a homophone of 'ARDOUR'.
(Other definitions for ardour that I've seen before include "Enthusiasm or warmth of passion" , "Love, passion" , "Burning desire" , "Love and enthusiasm" , "Great warmth of feeling or love" .)