Checking wood cut by saw (8)
I believe the answer is:
assaying
'checking' is the definition.
(assaying is testing the quality of a metal)
'wood cut by saw' is the wordplay.
'wood' becomes 'ash' (wood from an ash tree).
'cut' means to remove the last letter.
'by' is a charade indicator (letters next to each other).
'saw' becomes 'saying' (a saw can mean a proverb or maxim).
'ash' with its last letter taken off is 'as'.
'as'+'saying'='ASSAYING'
(Other definitions for assaying that I've seen before include "Analysing the composition of metal" , "Evaluating" , "Testing" , "Analyzing to determine properties" , "Analysing to determine properties" .)