Troy departing from barren island (4)
I believe the answer is:
sark
'island' is the definition.
(I've seen this before)
'troy departing from barren' is the wordplay.
'troy' becomes 't'.
'departing from' suggests deleting specific letters.
'barren' becomes 'stark' (I've seen this in another clue).
'stark' with 't' removed is 'SARK'.
(Other definitions for sark that I've seen before include "Island in English Channel" , "Small Channel Island" , "See 4 Down" , "Shirt (Sc.); Ch. island" , "Hereditarily-ruled Channel Island" .)