One agreement for model (5)
I believe the answer is:
ideal
'for model' is the definition.
(I know that good example is a type of ideal)
'one agreement' is the wordplay.
'one' becomes 'i' (Roman numeral).
'agreement' becomes 'deal' (deal is a kind of agreement).
'i'+'deal'='IDEAL'
(Other definitions for ideal that I've seen before include "highly desirable" , "immaculate" , "Just perfect, couldn't be better" , "Cutting/stabbing weapons" , "Paradigm" .)