As dye plant, use some vanilla (4)
I believe the answer is:
anil
'as dye' is the definition.
'anil' can be an answer for 'dye' (I've seen this in another clue). I am unsure of the 'as' bit.
'plant use some vanilla' is the wordplay.
'ANIL' is hidden within the letters.
But, I am uncertain how the hidden word is indicated.
(Other definitions for anil that I've seen before include "Shrub providing indigo" , "Shrub yielding indigo" , "West Indian shrub, source of indigo" , "Indigo (plant or dye)" , "It produces dye" .)