Motor originally bought by relative is a gem (9)
I believe the answer is:
carbuncle
'gem' is the definition.
(I know that carbuncle is a type of garnet)
'motor originally bought by relative' is the wordplay.
'motor' becomes 'car' (informal term for car).
'originally' says to take the initial letters.
'by' means one lot of letters go next to another.
'relative' becomes 'uncle' (uncle is a kind of relative).
The first letter of 'bought' is 'b'.
'car'+'b'+'uncle'='CARBUNCLE'
'is a' is the link.
(Other definitions for carbuncle that I've seen before include "Architectural eyesore" , "eyesore architecturally" , "Large boil-like inflammation - gemstone" , "Severe abscess in the skin" , "stone" .)