Ultimately elegant relative is tease (5)
I believe the answer is:
taunt
'is tease' is the definition.
(I've seen this before)
'ultimately elegant relative' is the wordplay.
'ultimately' suggests the final letters.
'relative' becomes 'aunt' (aunt is a kind of relative).
The last letter of 'elegant' is 't'.
't'+'aunt'='TAUNT'
(Other definitions for taunt that I've seen before include "Bait with insulting remarks" , "Thing said to anger or wound" , "Make fun of" , "Jeering remark" , "Jeer, deride" .)