Terribly odd jewel of a car (6)
I believe the answer is:
dodgem
'a car' is the definition.
(I've seen this before)
'terribly odd jewel' is the wordplay.
'terribly' is an anagram indicator.
'jewel' becomes 'gem' (synonyms).
'odd' with letters rearranged gives 'dod'.
'dod'+'gem'='DODGEM'
'of' is the link.
(Other definitions for dodgem that I've seen before include "Fairground amusement vehicle" , "ride - with 14a" , "Small car at funfair for bumping into others" , "Electric car" , "Bumper car" .)