Expansive, immense (4)
I believe the answer is:
vast
This clue is a double definition.
'expansive' is the first definition.
(I've seen this in another clue)
'immense' is the second definition.
(I know that immense can be written as vast)
(Other definitions for vast that I've seen before include "Extremely large or extensive" , "Of very great extent" , "Colossal" , "Huge, enormous" , "'Huge, immense (4)'" .)