Small volume about one pursuing girl is a masterpiece (7)
I believe the answer is:
'a masterpiece' is the definition.
(I have seen 'Literary masterpiece ' mean 'classic' so perhaps 'masterpiece' could also mean 'classic')
'small volume about one pursuing girl' is the wordplay.
'small volume' becomes 'cc' (cubic centimetre).
'about' indicates putting letters inside.
'one' becomes 'i' (Roman numeral).
'pursuing' means one lot of letters go next to another.
'girl' becomes 'lass' (lass is a kind of girl**).
'i' put after 'lass' is 'lassi'.
'cc' placed around 'lassi' is 'CLASSIC'.
'is' is the link.
(Other definitions for classic that I've seen before include "Great piece of creative writing" , "Literary masterpiece" , "major tournament" , "Oaks perhaps" , "Flat race" .)