Max ___, German artist who married artistic patron Peggy Guggenheim in 1942 (5)
I believe the answer is:
ernst
(Other definitions for ernst that I've seen before include "He painted" , "Max __; Dadaist" , "German-born painter, Max, co-founder of dadaism, d. 1976" , "Young partner" , "Max -, twentieth century German Surrealist artist" .)