Animal trap designed to hold one (5)
I believe the answer is:
tapir
'animal' is the definition.
(I've seen this before)
'trap designed to hold one' is the wordplay.
'designed' indicates an anagram (designed with the letters).
'to hold' is an insertion indicator.
'one' becomes 'i' (Roman numeral).
'trap' with letters rearranged gives 'tapr'.
'tapr' enclosing 'i' is 'TAPIR'.
(Other definitions for tapir that I've seen before include "Nocturnal hoofed animal" , "Hoofed mammal; I trap (anag.)" , "Long-nosed, hoofed mammal" , "nocturnal beast" , "I part with the pig-like animal" .)