Chilling in taxi flanked by horse (7)
I believe the answer is:
macabre
'chilling' is the definition.
(I've seen this before)
'taxi flanked by horse' is the wordplay.
'taxi' becomes 'cab' (synonyms).
'flanked by' is an insertion indicator (other letters go on other side).
'horse' becomes 'mare' (mare is a kind of horse).
'cab' inserted inside 'mare' is 'MACABRE'.
'in' acts as a link.
(Other definitions for macabre that I've seen before include "gruesome result" , "Gruesome, morbid" , "Gruesome and weird" , "Dark and disturbing" , "Ghostly appearance" .)