Game a dunderhead finished level (4)
I believe the answer is:
tied
'finished level' is the definition.
'tied' can be an answer for 'level' (thesaurus). I am not certain of the 'finished' bit.
'game a dunderhead' is the wordplay.
'game' becomes 'tie' (I've seen this before).
'a dunderhead' becomes 'd' (head letter of 'dunder').
'tie'+'d'='TIED'
Can you help me to learn more?
(Other definitions for tied that I've seen before include "eg Scored 1-1" , "United" , "Restricted, bound" , "With an equal score" , "Made bow" .)