Needle from small tree (5)
I believe the answer is:
spine
'needle' is the definition.
(thesaurus)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for spine that I've seen before include "Strength of character" , "Backbone" , "Part of book's jacket" , "Vertebral column" , "Thorn" .)