Trial of alternative timber (6)
I believe the answer is:
ordeal
'trial' is the definition.
(I've seen this before)
'alternative timber' is the wordplay.
'alternative' becomes 'or'.
'timber' becomes 'deal' (deal is a kind of timber).
'or'+'deal'='ORDEAL'
'of' acts as a link.
(Other definitions for ordeal that I've seen before include "Prolonged suffering, difficult to endure" , "Difficult or arduous experience" , "Severe or trying experience" , "Severe trial" , "A difficult and harrowing experience" .)