Tree-dwelling wild boar? True! (8)
I believe the answer is:
arboreal
'tree-dwelling' is the definition.
(I've seen this before)
'wild boar? true' is the wordplay.
'wild' is an anagram indicator.
'true' becomes 'real' (synonyms).
'boar' is an anagram of 'arbo'.
'arbo'+'real'='ARBOREAL'
(Other definitions for arboreal that I've seen before include "living in forest" , "Tree-dwelling" , "Pertaining to trees" , "Living among trees" , "Relating to trees" .)