Huge island, eastern, occupied by a thousand soldiers (7)
I believe the answer is:
immense
'huge' is the definition.
(I know that huge can be written as immense)
'island eastern occupied by a thousand soldiers' is the wordplay.
'island' becomes 'is' (abbreviation).
'eastern' becomes 'e'.
'occupied by' indicates putting letters inside.
'a thousand' becomes 'M' (Roman numeral for a thousand).
'soldiers' becomes 'men' (men can mean a group of soldiers).
'is'+'e'='ise'
'm'+'men'='mmen'
'ise' going around 'mmen' is 'IMMENSE'.
(Other definitions for immense that I've seen before include "Vast or enormous" , "Unusually great in size" , "Unctuously ingratiating" , "'Vast, colossal (7)'" , "Very big, exceedingly great" .)