Massive lobsters, and raw gulper eels for starters (5)
I believe the answer is:
large
'massive' is the definition.
('large' can be similar in meaning to 'massive')
'lobsters and raw gulper eels for starters' is the wordplay.
'for starters' indicates taking the first letters.
The initial letters of 'lobsters and raw gulper eels' is 'LARGE'.
(Other definitions for large that I've seen before include "Big, great" , "Above average in size, number, etc." , "Regal (anag)" , "Generous" , "Lake" .)