Extremely cold car - it buckled rear-end of Cadillac (6)
I believe the answer is:
arctic
'extremely cold' is the definition.
(I've seen this before)
'car it buckled rear-end of cadillac' is the wordplay.
'it' becomes ''t' (abbreviation. e.g. in 'tis).
'buckled' indicates anagramming the letters.
'rear end of cadillac' becomes 'ic' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'car'+'t'='cart'
'cart' with letters rearranged gives 'arct'.
'arct'+'ic'='ARCTIC'
Can you help me to learn more?
(Other definitions for arctic that I've seen before include "-- Circle; -- fox" , "Of the extreme north" , "Relating to the North Pole area" , "Northern ocean" , "Region around the North Pole" .)