One sort of wood is perfect (5)
I believe the answer is:
ideal
'is perfect' is the definition.
(similar in meaning)
'one sort of wood' is the wordplay.
'one' becomes 'I' (Roman numeral).
'sort of wood' becomes 'deal'.
'i'+'deal'='IDEAL'
(Other definitions for ideal that I've seen before include "just the job" , "Optimum" , "'Perfect, model (5)'" , "Exemplary" , "Perfect but perhaps unlikely to become reality" .)