Duke's wife skipping half of dull musical (5)
I believe the answer is:
chess
'musical' is the definition.
(Benny Andersson and Bjrn Ulvaeus musical)
I can't explain the rest of the clue.
(Other definitions for chess that I've seen before include "Benny Andersson and Bjorn Ulvaeus musical" , "Ancient war game whose name may have derived for the Persian for 'king'" , "This is played on board" , "form of battle" , "Sixteen-men-a-side game" .)