Gem of a motor bought initially by relative (9)
I believe the answer is:
carbuncle
'gem' is the definition.
(carbuncle is a kind of gem)
'a motor bought initially by relative' is the wordplay.
'a motor' becomes 'car' (I've seen this before).
'initially' says to take the initial letters.
'by' is a charade indicator (letters next to each other).
'relative' becomes 'uncle' (uncle is a kind of relative**).
The initial letter of 'bought' is 'b'.
'car'+'b'+'uncle'='CARBUNCLE'
'of' is the link.
(Other definitions for carbuncle that I've seen before include "stone" , "Cluster of boils - jewel" , "Skin eruption - gemstone" , "National Gallery's Sainsbury Wing?" , "Architectural eyesore" .)