Marcel Duchamp was probably the best-known artist in this iconoclastic movement (4)

I believe the answer is:
dada
(Other definitions for dada that I've seen before include "short-lived artistic movement" , "Early 20th-century arts movement, emphasizing the absurd" , "Irreverent Twentieth Century art movement" , "Nihilistic 20th-century European art movement" , "Precursor of surrealism" .)