Imbecile split on doctor working (6)
I believe the answer is:
drongo
'imbecile' is the definition.
(Australian term for a foolish person)
'split on doctor working' is the wordplay.
'split' becomes 'go' (split can mean to run away or leave).
'on' says to put letters next to each other.
'doctor' becomes 'Dr' (synonyms).
'working' becomes 'on'.
'dr'+'on'='dron'
'go' after 'dron' is 'DRONGO'.
(Other definitions for drongo that I've seen before include "Bird -- idiot (in Australia)" , "dope" , "Australian fool - Gordon (anag)" , "Bird - Aussie fool - Gordon (anag)" , "Long-tailed songbird" .)