Old record book in which the writer's found archetype (7)
I believe the answer is:
epitome
'archetype' is the definition.
(thesaurus)
'old record book in which the writer's' is the wordplay.
'old record' becomes 'ep'.
'book' becomes 'tome' (tome is a kind of book).
'in which' means one lot of letters goes inside another.
'the writer' becomes 'i' (the person who is writing these clues).
'ep'+'tome'='eptome'
'eptome' placed around 'i' is 'EPITOME'.
'found' is the link.
(Other definitions for epitome that I've seen before include "classic example" , "Embodiment, type" , "Something embodying perfectly a stated quality or idea" , "ie Tempo (anag.)" , "Paradigm" .)