A huge carriage and it can shift! (8)
I believe the answer is:
gigantic
'a huge' is the definition.
(I've seen this before)
'carriage and it can shift' is the wordplay.
'carriage' becomes 'gig' (gig is a kind of carriage).
'and' is a charade indicator (letters next to each other).
'shift' indicates an anagram.
'it'+'can'='itcan'
'itcan' anagrammed gives 'antic'.
'gig'+'antic'='GIGANTIC'
(Other definitions for gigantic that I've seen before include "Fantastically great" , "Hugh,colossal" , "Great big" , "monster" , "Huge, enormous" .)