Animal with horn, I gathered (5)
I believe the answer is:
rhino
'animal' is the definition.
(short for rhinoceros)
'with horn i gathered' is the wordplay.
'with' means one lot of letters go next to another.
'gathered' indicates anagramming the letters (the letters are gathered into a new order).
'horn' put next to 'i' is 'horni'.
'horni' is an anagram of 'RHINO'.
(Other definitions for rhino that I've seen before include "Ready" , "Horny creature" , "Powerful herbivorous odd-toed ungulate, informally" , "Moola" , "The necessary" .)