Black bird and bear (5)
I believe the answer is:
brook
'bear' is the definition.
(both can mean to tolerate or endure)
'black bird' is the wordplay.
'black' becomes 'b' (as in pencil classifications).
'bird' becomes 'rook' (rook is a kind of bird).
'b'+'rook'='BROOK'
'and' is the link.
(Other definitions for brook that I've seen before include "Small fresh-water stream" , "Bear - small stream" , "running water" , "Stand for" , "stomach" .)