Animal doctor poses naked (5)
I believe the answer is:
moose
'animal' is the definition.
(thesaurus)
'doctor poses naked' is the wordplay.
'doctor' becomes 'mo' (medical officer).
'naked' means to look at the middle letters.
The centre of 'poses' is 'ose'.
'mo'+'ose'='MOOSE'
(Other definitions for moose that I've seen before include "Large US deer" , "beasts" , "Large northern deer" , "US deer with enormous antlers" , "North American elk" .)