Appropriate to let raven roam (8)
I believe the answer is:
relevant
'appropriate' is the definition.
(I've seen this before)
'let raven roam' is the wordplay.
'roam' indicates an anagram (I've seen 'roaming' mean this).
'let'+'raven'='letraven'
'letraven' with letters rearranged gives 'RELEVANT'.
'to' acts as a link.
(Other definitions for relevant that I've seen before include "Material" , "Suitable" , "Bearing on the issue in hand" , "Related to the matter in hand" , "Appropriate" .)