Place for a plant (4)
I believe the answer is:
sill
'place for a plant' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for sill that I've seen before include "Underwater rock ledge" , "Shelf at the foot of a window" , "Slab at foot of window" , "Mass of rock" , "Ledge beneath a window" .)