Picasso's movement (6)
I believe the answer is:
cubism
'picasso's movement' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for cubism that I've seen before include "A modern art movement" , "Art style using geometrical shapes" , "C 20 painting style (Braque, Picasso)" , "Style of e.g. Braque" , "Artistic movement for which Picasso was famous" .)