Saw son cut down to 1, for easier assimilation (7)
I believe the answer is:
spotted
'saw' is the definition.
(I've seen this before)
I don't understand how the rest of the clue works.
(Other definitions for spotted that I've seen before include "Caught sight of; dotty" , "Saw, caught sight of" , "Saw; speckled" , "Seen; saw" , "Saw; mottled" .)