Refuse tea by significant volume (5)
I believe the answer is:
chaff
'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" .)