Adriatic, e.g. (3)
I believe the answer is:
sea
'adriatic eg' is the definition.
(adriatic is a kind of sea)
This is all the clue.
(Other definitions for sea that I've seen before include "Ocean area" , "The briny" , "& 14 Ozone" , "Large expanse of water" , "It's stocked with fish" .)