Protective garment’s key for entering wood (8)
I believe the answer is:
'protective garment's' is the definition.
(I've seen this before)
'key for entering wood' is the wordplay.
'key' becomes 'A' (musical key).
'entering' means one lot of letters goes inside another.
'wood' becomes 'pine' (pine is a type of wood).
'afor' put into 'pine' is 'PINAFORE'.
(Other definitions for pinafore that I've seen before include "Protective gear" , "Protective garment worn over front" , "Sleeveless dress or apron" , "gives homely protection" , "Protective kitchen wear" .)