The Friendly Islands national wears classical garment
I believe the answer is:
tonga
'the friendly islands' is the definition.
(I've seen this before)
'national wears classical garment' is the wordplay.
'national' becomes 'n' (abbreviation listed in Chambers).
'wears' indicates putting letters inside.
'classical garment' becomes 'toga' (I've seen this before).
'n' inserted inside 'toga' is 'TONGA'.
(Other definitions for tonga that I've seen before include "Pacific island state" , "Light vehicle in India" , "Polynesian island" , "SW Pacific monarchy" , "transport" .)