Thorny tree
I believe the answer is:
acacia
'thorny tree' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for acacia that I've seen before include "Plant like wattle" , "Flowering shrub of the pea family" , "Spiny tree of warm climates" , "Australian tree" , "Wattle genus" .)