Relative entering Highland dance and showing off (9)
I believe the answer is:
flaunting
'showing off' is the definition.
('flaunt' can be a synonym of 'show off')
'relative entering highland dance' is the wordplay.
'relative' becomes 'aunt' (aunt is a type of relative).
'entering' is an insertion indicator.
'highland dance' becomes 'fling' (I've seen this before).
'aunt' placed inside 'fling' is 'FLAUNTING'.
'and' acts as a link.
(Other definitions for flaunting that I've seen before include "Ostentatiously displaying" , "Showing off" .)