One sort of wood that's without flaws (5)
I believe the answer is:
ideal
'without flaws' is the definition.
(I've seen this before)
'one sort of wood' is the wordplay.
'one' becomes 'i' (Roman numeral).
'sort of wood' becomes 'deal'.
'i'+'deal'='IDEAL'
'that's' is the link.
(Other definitions for ideal that I've seen before include "superb specimen" , "that can't be bettered?" , "principle to be aimed at" , "Coal-mining waste" , "Perfectly suited" .)