Briny deep (3)
I believe the answer is:
sea
'briny deep' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for sea that I've seen before include "The Med, e.g." , "E.g. Yellow, Red area" , "North, say" , "It's stocked with fish" , "Vast expanse" .)