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' means one lot of letters goes inside another.
'highland dance' becomes 'fling' (I've seen this before).
'aunt' going inside 'fling' is 'FLAUNTING'.
'and' is the link.
(Other definitions for flaunting that I've seen before include "Ostentatiously displaying" , "Showing off" .)