Green sauce (5)
I believe the answer is:
pesto
'green sauce' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for pesto that I've seen before include "Sauce made of basil and cheese" , "sauce involving Basil" , "Pasta sauce variety" , "Sauce of basil, pine nuts, etc" , "Pasta sauce mainly of basil and cheese" .)