Trap designed to catch one animal (5)
I believe the answer is:
tapir
'animal' is the definition.
(tapir is a type of animal)
'trap designed to catch one' is the wordplay.
'designed' indicates an anagram (designed with the letters).
'to catch' indicates putting letters inside.
'one' becomes 'i' (Roman numeral).
'trap' with letters rearranged gives 'tapr'.
'tapr' going around 'i' is 'TAPIR'.
(Other definitions for tapir that I've seen before include "Nocturnal hoofed animal" , "A trip (anag) - animal" , "Hoofed mammal; I trap (anag.)" , "Nocturnal mammal with a short flexible proboscis" , "Long-nosed, hoofed mammal" .)