Conker tree (5,8)
I believe the answer is:
horse chestnut
'conker tree' is the definition.
(I know that conker tree can be written as horse-chestnut)
This is the entire clue.
(Other definitions for horse chestnut that I've seen before include "inedible fruit" , "Tree with conkers" , "It bears fruit" , "Common British tree" , "Type of tree" .)