Crossword compiler might need this work out -- one's dumpy (9)
I believe the answer is:
pseudonym
'crossword compiler might need this work' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how one could define the other.
'out one's dumpy' is the wordplay.
'out' is an anagram indicator.
'ones'+'dumpy'='onesdumpy'
'onesdumpy' with letters rearranged gives 'PSEUDONYM'.
Can you help me to learn more?
(Other definitions for pseudonym that I've seen before include "Lewis Carroll, perhaps?" , "Pen-name" , "Our cryptic crossword always carries one" , "another title" , "Cinephile, for one" .)