Caviar base (3)
I believe the answer is:
roe
'caviar base' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for roe that I've seen before include "Caviar" , "Swift runner" , "Mass of fish's eggs" , "Fish eggs; small deer" , "Part of fish, sounds like go through water" .)