All right, a sanctimonious creature (5)
I believe the answer is:
okapi
'creature' is the definition.
(African mammal)
'all right a sanctimonious' is the wordplay.
'all right' becomes 'ok' (synonyms).
'sanctimonious' becomes 'pi' (British abbreviation for pious).
'ok'+'a'+'pi'='OKAPI'
(Other definitions for okapi that I've seen before include "African leaves fancier" , "Ruminant mammal of Africa" , "Small giraffe" , "Rare mammal" , "African mammal related to giraffe" .)