Cars can turn in them (4)
I believe the answer is:
arcs
'turn in them' is the definition.
I can't tell whether this defines the answer.
'cars can' is the wordplay.
'can' indicates anagramming the letters (I've seen 'canned' mean this (canned can mean drunk)).
'cars' anagrammed 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" .)