Novelist about fifty? Not quite (6)
I believe the answer is:
hardly
'not quite' is the definition.
(thesaurus)
'novelist about fifty?' is the wordplay.
'novelist' becomes 'hardy' (Hardy is a novelist).
'about' indicates putting letters inside.
'fifty?' becomes 'l' (roman numeral).
'hardy' placed around 'l' is 'HARDLY'.
(Other definitions for hardly that I've seen before include "Not much" , "Almost not" , "Barely, scarcely" , "Not quite "It seems unlikely!"" , "With great difficulty" .)