The Three Musketeers author (5)
I believe the answer is:
'the three musketeers author' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for dumas that I've seen before include "Musketeers writer" , "French novelist" , "French pair who wrote" , "Author of The Three Musketeers" , "of house in Moscow" .)