Ghastly creature pinching taxi (7)
I believe the answer is:
macabre
'ghastly' is the definition.
(synonyms)
'creature pinching taxi' is the wordplay.
'creature' becomes 'mare' (female horse).
'pinching' is an insertion indicator (taking inside).
'taxi' becomes 'cab' (synonyms).
'mare' going around 'cab' is 'MACABRE'.
(Other definitions for macabre that I've seen before include "Gruesome, morbid" , "gruesome result" , "Shockingly horrible" , "'Grisly, gruesome (7)'" , "Gruesome and weird" .)