Alfalfa (7)
I believe the answer is:
lucerne
'alfalfa' is the definition.
(synonyms)
This is all the clue.
(Other definitions for lucerne that I've seen before include "Source of chlorophyll" , "Clover-like plant used for fodder" , "Swiss city/lake" , "Forage crop" , "Alfalfa - Swiss lake and resort" .)