Plant essence of oils in resin (5)
I believe the answer is:
lilac
'plant' is the definition.
(type of plant)
'essence of oils in resin' is the wordplay.
'essence of' indicates the central letters.
'in' indicates putting letters inside.
'resin' becomes 'lac' (resin secreted by lac insects).
The middle letters of 'oils' are 'il'.
'il' put within 'lac' is 'LILAC'.
(Other definitions for lilac that I've seen before include "Fragrant shrub; colour" , "Flower celebrated by Schubert" , "Tree - pinkish-purple colour" , "Fragrant,purple flower" , "Pale mauve colour for a flower" .)