Cars can turn in them (4)
I believe the answer is:
arcs
'turn in them' is the definition.
I can't judge whether this defines the answer.
'cars can' is the wordplay.
'can' is an anagram indicator (I've seen 'canned' mean this (canned can mean drunk)).
'cars' with letters rearranged gives 'ARCS'.
Can you help me to learn more?
(Other definitions for arcs that I've seen before include "Parts of a circle" , "Curves in cars" , "Segments of a circle" , "Streaks of electrical discharges" , "formations not straight" .)