Vast, colossal (7)
I believe the answer is:
immense
I believe this is a double definition.
'vast' is the first definition.
(I've seen this before)
'colossal' is the second definition.
(synonyms)
(Other definitions for immense that I've seen before include "'Gigantic, extensive (7)'" , "Unusually large or great" , "Mammoth" , "Vast or enormous" , "Very good" .)