Convertible alternative (5)
I believe the answer is:
sedan
'convertible alternative' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for sedan that I've seen before include "Old portable chair for Danes" , "Covered seat carried by bearers" , "Palanquin; car" , "big chair" , "Covered chair carried between poles" .)