Axeman might use this initially entering copse, trying resolutely to cut tree (8)
I believe the answer is:
'axeman might use this' is the definition.
(axeman can mean a male rock guitarist)
'initially entering copse trying resolutely to cut tree' is the wordplay.
'initially' suggests taking the first letters.
'to cut' is an insertion indicator.
'tree' becomes 'plum' (plum tree is a kind of tree).
The initial letters of 'entering copse trying resolutely' is 'ectr'.
'ectr' going within 'plum' is 'PLECTRUM'.
(Other definitions for plectrum that I've seen before include "One for plucking guitar", "It's used to pluck, a guitar say", "Guitarist's implement", "Guitar pick", "Device for playing guitar".)