Brush, not having a plant (5)
I believe the answer is:
cress
'plant' is the definition.
(cress is a kind of plant)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for cress that I've seen before include "Salad plant paired with mustard" , "bit of salad" , "Cruciferous salad plant" , "Food item" , "Plant with pungent leaves used in salads" .)