Highland wear and outfit’s left inside (4)
I believe the answer is:
kilt
'highland wear' is the definition.
(I've seen this in another clue)
'outfit's left inside' is the wordplay.
'outfit' becomes 'kit' (kitting is a kind of outfiting).
'left' becomes 'l' (common abbreviation).
'inside' is an insertion indicator.
'kit' going around 'l' is 'KILT'.
'and' is the link.
(Other definitions for kilt that I've seen before include "Tartan skirt worn in Scotland" , "Scots garment" , "Under which, traditionally, a Scotsman wears nothing" , "Highland garb" , "Checked menswear" .)