Island also contains trap (6)
I believe the answer is:
tobago
'island' is the definition.
(Caribbean island)
'also contains trap' is the wordplay.
'also' becomes 'too' (synonyms).
'contains' indicates putting letters inside.
'trap' becomes 'bag' (I've seen this in another clue).
'too' enclosing 'bag' is 'TOBAGO'.
(Other definitions for tobago that I've seen before include "Trinidad and - (WI)" , "Trinidad companion island" , "West Indian island" , "Caribbean island" , "island location" .)