Sun clue faulty in central part (7)
I believe the answer is:
nucleus
'central part' is the definition.
(I've seen this before)
'sun clue faulty' is the wordplay.
'faulty' indicates an anagram.
'sun'+'clue'='sunclue'
'sunclue' is an anagram of 'NUCLEUS'.
'in' is the link.
(Other definitions for nucleus that I've seen before include "Heart of the Matter" , "Atom's core" , "atomic centre" , "Central core of an atom" , "Core, centre" .)