One sitting in car in outskirts of Croydon gets warning (7)
I believe the answer is:
caution
'warning' is the definition.
(caution is a kind of warning)
'one sitting in car in outskirts of croydon' is the wordplay.
'one' becomes 'i' (Roman numeral).
'sitting in' means one lot of letters goes inside another.
'car' becomes 'auto' ('auto' can be a synonym of 'car').
'in' is an insertion indicator.
'outskirts of' suggests removing the centre.
'croydon' with its middle removed is 'cn'.
'i' going inside 'auto' is 'autio'.
'autio' going within 'cn' is 'CAUTION'.
'gets' is the link.
(Other definitions for caution that I've seen before include "Heed - warning - funny person" , "Prudent wariness" , "Legal warning" , "Attention to possible danger" , "Hoot" .)