Pick clubs and hearts over diamonds (6)
I believe the answer is:
choice
'pick' is the definition.
(synonyms)
'clubs and hearts over diamonds' is the wordplay.
'clubs' becomes 'c' (abbreviation in card games).
'and' means one lot of letters go next to another.
'hearts' becomes 'h' (abbreviation used in card games e.g. bridge).
'over' becomes 'o' (cricket abbreviation).
'diamonds' becomes 'ice' (slang term for diamonds).
'c'+'h'+'o'+'ice'='CHOICE'
(Other definitions for choice that I've seen before include "Excellent" , "Act or power of selecting" , "Variety" , "'Option, alternative (6)'" , "'Selection, option (6)'" .)