High-spirited relative in borders of Jersey (6)
I believe the answer is:
jaunty
'high-spirited' is the definition.
(thesaurus)
'relative in borders of jersey' is the wordplay.
'relative' becomes 'aunt' (aunt is a kind of relative).
'in' means one lot of letters goes inside another.
'borders of' means to remove the middle letters.
'jersey' with its middle taken out is 'jy'.
'aunt' inserted into 'jy' is 'JAUNTY'.
(Other definitions for jaunty that I've seen before include "Stylish" , "Happy" , "Sprightly and cheerful" , "With a lively self-confident manner" , "Cheerful and self-confident, perhaps with a swagger" .)