Yellowish-green finch (6)
I believe the answer is:
siskin
'yellowish-green finch' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for siskin that I've seen before include "Small yellow and black finch" , "Greenish songbird of finch family" , "Yellow-green finch" , "Yellowish-green finch" , "Finch akin to canary" .)