A wild animal but it's all right, a quiet one (5)
I believe the answer is:
okapi
'a wild animal' is the definition.
(I've seen this before)
'it's all right a quiet one' is the wordplay.
'it's all right' becomes 'ok' (synonyms).
'quiet' becomes 'p' (music symbol for 'piano', ie soft or quiet).
'one' becomes 'i' (Roman numeral).
'ok'+'a'+'p'+'i'='OKAPI'
'but' is the link.
(Other definitions for okapi that I've seen before include "Wild animal" , "Native of Central Africa" , "Type of giraffe" , "Central Afr. ruminant" , "Mammal of giraffe family" .)