Some tallish rubber plant (5)
I believe the answer is:
shrub
'plant' is the definition.
(type of plant)
'some tallish rubber' is the wordplay.
'some' indicates the answer is hidden within the clue (some parts of the word are used).
'SHRUB' is hidden within 'tallish rubber'.
(Other definitions for shrub that I've seen before include "Perhaps Heather" , "Myrtle or Rosemary, say" , "Cordial" , "Hazel perhaps" , "Woody plant, bush" .)