Parentheses' shapes (4)
I believe the answer is:
arcs
'parentheses' shapes' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for arcs that I've seen before include "Streaks of electrical discharges" , "Portions of a circle" , "Parts of a circle" , "Parts of a curve" , "formations not straight" .)