Indigo shrub (4)
I believe the answer is:
anil
'indigo shrub' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for anil that I've seen before include "Species of blue" , "West Indian shrub, source of indigo" , "name of man" , "Shrub providing indigo" , "Shrub yielding indigo" .)