Creature less cold in the East End (5)
I believe the answer is:
'creature' is the definition.
(I've seen this before)
'less cold in the east end' is the wordplay.
'less cold' becomes 'hotter' ('hot' can be the opposite of 'cold' so perhaps 'hotter' is reasonable for 'less cold').
'in the east end' means to remove the first letter (drop a letter, as a cockney might).
'hotter' with its initial letter removed is 'OTTER'.
(Other definitions for otter that I've seen before include "Fish-eater of the weasel family" , "Water creature" , "Fish-eating water animal with brown fur and flat tail" , "Mine is made safe by this" , "Carnivorous aquatic mammal" .)