Guy manufactured synthetic (3-4)
I believe the answer is:
man-made
'synthetic' is the definition.
(I know that synthetic can be written as man-made)
'guy manufactured' is the wordplay.
'guy' becomes 'man' (guy can informally mean a man).
'manufactured' becomes 'made' (I've seen this before).
'man'+'made'='MAN-MADE'
(Other definitions for man-made that I've seen before include "Constructed by humans, not by nature" , "Artificial, synthetic" , "Caused by humans" .)