Knight wearing Roman garment in the Friendly Islands (5)
I believe the answer is:
tonga
'the friendly islands' is the definition.
(I've seen this before)
'knight wearing roman garment' is the wordplay.
'knight' becomes 'n' (chess).
'wearing' is an insertion indicator.
'roman garment' becomes 'toga' (I've seen this before**).
'n' going into 'toga' is 'TONGA'.
'in' is the link.
(Other definitions for tonga that I've seen before include "Two-wheeled Indian vehicle" , "Relatively small" , "Polynesian island" , "part of Polynesia" , "group of Pacific islands" .)