Crossword Genius

Refuse tea by significant volume (5)

Ross

I believe the answer is:

chaff

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'refuse' is the definition.
(I've seen this before)

'tea by significant volume' is the wordplay.
'tea' becomes 'cha' (cha is a type of tea).
'by significant volume' becomes 'ff' (I can't justify this - if you can you should believe this answer much more).
'cha'+'ff'='CHAFF'

Can you help me to learn more?

(Other definitions for chaff that I've seen before include "Tease in good-humoured way" , "something worth little" , "Shucks" , "Corn husks - worthless stuff" , "Laugh at" .)

I've seen this clue in the Sydney Morning Herald.
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