Buck up to win final of tennis slam (5)
I believe the answer is:
trash
'slam' is the definition.
The answer and definition can be both related to communication as well as being singular nouns.
Maybe there's an association between them I don't understand?
'buck up to win final of tennis' is the wordplay.
'buck' becomes 'hart' (I can't justify this - if you can you should give a lot more credence to this answer).
'up' is a reversal indicator (in down clue: letters go upwards).
'to win' means one lot of letters goes inside another (some letters win or obtain others).
'final of' says to take the final letters (I've seen 'final' mean this).
The last letter of 'tennis' is 's'.
'hart' reversed gives 'trah'.
'trah' going around 's' is 'TRASH'.
Can you help me to learn more?
(Other definitions for trash that I've seen before include "Take the tops from < rhubarb" , "Dismiss as valueless" , "bull" , "Drivel" , "Worthless people; destroy (US slang)" .)