Frightful horn is core to identify this animal (10)
I believe the answer is:
rhinoceros
'this animal' is the definition.
(thesaurus)
'frightful horn is core' is the wordplay.
'frightful' indicates an anagram (I've seen this in other clues).
'horn'+'is'+'core'='horniscore'
'horniscore' is an anagram of 'RHINOCEROS'.
'to identify' is the link.
(Other definitions for rhinoceros that I've seen before include "Pachyderm" , "Endangered animal" , "Native of Africa" , "Horned ungulate" , "Large, thick-skinned ungulate" .)