Trim good book about ancestor? (6)
I believe the answer is:
parent
'ancestor?' is the definition.
(I know that parent is a type of biological parent)
'trim good book' is the wordplay.
'trim' becomes 'pare' (synonyms).
'good book' becomes 'NT' (New Testament).
'pare'+'nt'='PARENT'
'about' is the link.
(Other definitions for parent that I've seen before include "Begetter of offspring" , "One with children" , "The company of which others are subsidiaries" , "Mother or father or what they do" , "person responsible for children" .)