Maui or Oahu (4)
I believe the answer is:
isle
'maui or oahu' is the definition.
(I know that Maui is a high island)
This is the entire clue.
(Other definitions for isle that I've seen before include "eg Man, Wight" , "it's offshore" , "somewhere surrounded by water" , "Man's one" , "Sea-girt land" .)