Asian legume (4)
I believe the answer is:
soya
'asian legume' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for soya that I've seen before include "Plant seed, meat substitute" , "It's used as a substitute for animal protein" , "Asian bean yielding edible oil and flour" , "Dark salty sauce" , "Plant grown for its beans" .)