A selfish desire to get something done! (6)
I believe the answer is:
agreed
'something done' is the definition.
(done or resolved)
'a selfish desire' is the wordplay.
'selfish desire' becomes 'greed' (I've seen this in another clue).
'a'+'greed'='AGREED'
'to get' acts as a link.
(Other definitions for agreed that I've seen before include "Done!" , "Expressed willingness" , "Accorded" , "Was consistent" , "Okayed" .)