Sadly part with one animal (5)
I believe the answer is:
tapir
'animal' is the definition.
(tapir is a type of animal)
'sadly part with one' is the wordplay.
'sadly' indicates anagramming the letters.
'with' means one lot of letters goes inside another.
'one' becomes 'I' (Roman numeral).
'part' with letters rearranged gives 'tapr'.
'tapr' going around 'i' is 'TAPIR'.
(Other definitions for tapir that I've seen before include "A trip (anag) - animal" , "Ungulate" , "Hoofed mammal; I trap (anag.)" , "Browser" , "Animal with elongated snout" .)