Spiny shrub (5)
I believe the answer is:
gorse
'spiny shrub' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for gorse that I've seen before include "Spiny yellow-flowered shrub" , "Spiny heathland shrub" , "Wild shrub with yellow flowers and sharp thorns, common on hillsides" , "Prickly shrub with yellow flowers" , "Prickly heath shrub" .)