Emerald ___ (4)
(Other definitions for isle that I've seen before include "This is sceptred!" , "Detached territory" , "See 11 Across" , "It lies badly in water" , "Eg, eyot or inch" .)
'emerald' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for beryl that I've seen before include "Girl" , "Precious stone of which emerald is a variety" , "- - Bainbridge (lit.)" , "Pale greenish" , "Coloured stone" .)