Yellowish green (4)
I believe the answer is:
lime
'yellowish green' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for lime that I've seen before include "Tree; alkali" , "Acid green fruit like a lemon" , "Mailed item" , "Sharp-tasting fruit" , "Citrus fruit - shade of green" .)