He’s presumably bearable (5)
I believe the answer is:
teddy
'he's presumably bearable' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.
'he's presumably bearable' is the wordplay.
'he' becomes 'ted'.
'presumably bearable' becomes 'dy' (I am not sure about this - if you are sure you should believe this answer much more).
'ted'+'dy'='TEDDY'
Can you help me to learn more?
(Other definitions for teddy that I've seen before include "Child's soft toy" , "Stuffed bear" , "Cuddly toy" , "Bear - boy" , "A child's toy bear" .)