That chap making a chimney piece (3)
I believe the answer is:
him
'that chap' is the definition.
(I've seen this in another clue)
'making a chimney piece' is the wordplay.
'piece' indicates a hidden word.
'HIM' is hidden in the letters of 'making chimney'.
(Other definitions for him that I've seen before include "Objective male pronoun" , "Proper character" , "That man" .)