Dada pioneer Max (5)
I believe the answer is:
ernst
'dada pioneer max' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for ernst that I've seen before include "Max __; Dadaist" , "German-born painter, Max, co-founder of dadaism, d. 1976" , "Young partner" , "Max -, twentieth century German Surrealist artist" , "Surrealist; stern (anag.)" .)