Medicinal succulent (4)
I believe the answer is:
aloe
'medicinal succulent' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for aloe that I've seen before include "Bitter drug from a leaf juice" , "Succulent plant (may be bitter!)" , "Bitter fruit" , "Genus of bitter herbs" , "O, ale with bitter plant" .)