Test an alternative sort of timber (6)
I believe the answer is:
ordeal
'test' is the definition.
(I've seen this before)
'an alternative sort of timber' is the wordplay.
'an alternative' becomes 'or'.
'sort of timber' becomes 'deal'.
'or'+'deal'='ORDEAL'
(Other definitions for ordeal that I've seen before include "Tough test in Laredo" , "Unpleasant and prolonged experience" , "Torture" , "Severe or trying experience" , "very hard test" .)