Digitalis (8)
I believe the answer is:
foxglove
'digitalis' is the definition.
(synonyms)
This is the entire clue.
(Other definitions for foxglove that I've seen before include "Source of 1 dn" , "Flowering plant that's source of digitalis" , "Common wild flower" , "Plant (of the genus 10 down) with bell-shaped flowers" , "that grows wild" .)