Old toilet-trained literary parvenu (9)
I believe the answer is:
doolittle
'literary parvenu' is the definition.
The definition suggests a singular noun which matches the answer.
'old toilet-trained' is the wordplay.
'trained' is an anagram indicator (to train can mean to grow something into a shape).
'old'+'toilet'='oldtoilet'
'oldtoilet' with letters rearranged gives 'DOOLITTLE'.
Can you help me to learn more?
(Other definitions for doolittle that I've seen before include "dustman" , "Girl made grand" , "Cockney Eliza" , "Eliza ---, Higgins's pupil (G. B. Shaw)" , "flower seller" .)