Island nation involved in formal tailoring (5)
I believe the answer is:
malta
'island nation' is the definition.
(country made up of two islands)
'involved in formal tailoring' is the wordplay.
'involved in' indicates the answer is hidden within the clue.
'MALTA' is hidden within 'formal tailoring'.
(Other definitions for malta that I've seen before include "GC island" , "Mediterranean island, capital Valletta" , "seagirt republic" , "Island nation" , "Mediterranean country" .)