A bundle of nerves, band meets hero (8)
I believe the answer is:
ganglion
'a bundle of nerves' is the definition.
(group of nerve cells)
'band meets hero' is the wordplay.
'band' becomes 'gang' (I've seen this before).
'meets' is a charade indicator (letters next to each other).
'hero' becomes 'lion'.
'gang'+'lion'='GANGLION'
(Other definitions for ganglion that I've seen before include "that shows a bit of nerve" , "concentration of strength" , "Collection of nerve cells" , "Swelling" , "A longing for group of nerve cells" .)