Caribbean island not supporting Pacific island? Not entirely (7)
I believe the answer is:
antigua
'caribbean island' is the definition.
(I've seen this before)
'not supporting pacific island? not entirely' is the wordplay.
'not supporting' becomes 'anti' (I've seen this in another clue).
'pacific island?' becomes 'guam' (I've seen this before).
'not entirely' means to remove the last letter (most but not all of the word).
'guam' with its final letter taken away is 'gua'.
'anti'+'gua'='ANTIGUA'
(Other definitions for antigua that I've seen before include "Caribbean island linked with Barbuda" , "warm island" , "Aga unit in the West Indies" , "holiday destination" , "Largest of Leeward Is." .)