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