Sharp blade in copse initially seen on tree (7)
I believe the answer is:
acerbic
'sharp' is the definition.
(synonyms)
'blade in copse initially seen on tree' is the wordplay.
'initially' says to take the initial letters.
'seen on' is a charade indicator (letters next to each other).
'tree' becomes 'acer' (I've seen this before).
The initial letters of 'blade in copse' is 'bic'.
'bic' put after 'acer' is 'ACERBIC'.
(Other definitions for acerbic that I've seen before include "Cutting" , "Astringent; sour" , "Bitter in taste -- harsh in tone" , "Harsh and sharp in speech" , "Sharp, forthright" .)