Irregular - not even a good earner (6)
I believe the answer is:
oddjob
'even a good earner' is the definition.
I don't know anything about this answer so I can't judge whether this works.
'irregular not' is the wordplay.
'irregular' becomes 'odd'.
'not' becomes 'job' (I can't justify this - if you can you should believe this answer much more).
'odd'+'job'='ODDJOB'
Can you help me to learn more?
(Other definitions for oddjob that I've seen before include "casual work" , "Villainous character" , "henchman in film" .)