Car terribly hard to bend (4)
I believe the answer is:
arch
'to bend' is the definition.
(arching is a kind of bending)
'car terribly hard' is the wordplay.
'terribly' is an anagram indicator.
'hard' becomes 'h' (abbreviation used in pencil classifications).
'car' anagrammed gives 'arc'.
'arc'+'h'='ARCH'
(Other definitions for arch that I've seen before include "Mysterious - curve" , "a piece about a foot?" , "in short, is out of date" , "Waggish" , "one that may have fallen" .)