Fresh horn covers one animal (5)
I believe the answer is:
rhino
'animal' is the definition.
(short for rhinoceros)
'fresh horn covers one' is the wordplay.
'fresh' indicates an anagram.
'covers' means one lot of letters goes inside another.
'one' becomes 'i' (Roman numeral).
'horn' is an anagram of 'rhno'.
'rhno' enclosing 'i' is 'RHINO'.
(Other definitions for rhino that I've seen before include "Charging animal" , "Thick-skinned type" , "In brief, large thick-skinned animal of Africa" , "one still charges in Africa" , "one might charge in Africa" .)