Key work by artist that's a bit of a nut (5)
I believe the answer is:
copra
'a bit of a nut' is the definition.
(I've seen this before)
'key work by artist' is the wordplay.
'key' becomes 'c' (I've seen this in other clues).
'work' becomes 'op' (common abbreviation for 'opus').
'by' means one lot of letters go next to another.
'artist' becomes 'RA' (Royal Academician, member of Royal Academy of Arts).
'c'+'op'+'ra'='COPRA'
'that's' is the link.
(Other definitions for copra that I've seen before include "Dried coconut meat" , "Coconut's kernel" , "Nutty product" , "Dried cocoa-nut kernels, source of oil" , "Dried coconut kernels" .)