Substantial amount of timber? (4)
I believe the answer is:
deal
This might be a double definition.
'substantial amount' is the first definition.
'deal' can be an answer for 'amount' (deal is a kind of amount). I am unsure of the 'substantial' bit.
'timber?' is the second definition.
(deal is a kind of timber)
'of' is the link.
Can you help me to learn more?
(Other definitions for deal that I've seen before include "Distribute (cards); pine or fir timber" , "Distribute cards or do business" , "Distribute (cards); wood" , "Agreement; soft wood" , "Pass around (e.g. cards)" .)