Terribly brave, tree of bones (9)
I believe the answer is:
vertebrae
'bones' is the definition.
(vertebra is a kind of bone)
'terribly brave tree' is the wordplay.
'terribly' is an anagram indicator.
'brave'+'tree'='bravetree'
'bravetree' is an anagram of 'VERTEBRAE'.
'of' acts as a link.
(Other definitions for vertebrae that I've seen before include "Bony segments of the spinal column" , "Backbone segments" , "Bits of bone" , "Bits of skeleton" , "Bones of the spinal column" .)