Throw out black cat (6)
I believe the answer is:
bounce
'throw out' is the definition.
(bouncing is a kind of throwing out)
'black cat' is the wordplay.
'black' becomes 'b' (as in pencil classifications).
'cat' becomes 'ounce' (ounce is a kind of cat).
'b'+'ounce'='BOUNCE'
(Other definitions for bounce that I've seen before include "Of a cheque, send back as worthless" , "Springiness" , "Rebound; self-confidence" , "Reflect back from a surface" , "Throw out" .)