Beeb's unending concerts, originally with Henry Wood (5)
I believe the answer is:
beech
'wood' is the definition.
(beech is a kind of wood)
'beeb's unending concerts originally with henry' is the wordplay.
'unending' means to remove the last letter.
'originally' suggests taking the first letters.
'with' means one lot of letters go next to another.
'henry' becomes 'h' ('H' can be a synonym of 'henry').
The initial letter of 'concerts' is 'c'.
'beeb' with its final letter removed is 'bee'.
'bee'+'c'+'h'='BEECH'
(Other definitions for beech that I've seen before include "It has branches" , "for mast?" , "Tree variety" , "Nut-bearing tree" , "Tree (with green or copper leaves)" .)