Volume of whispers picked up (4)
I believe the answer is:
size
'volume' is the definition.
(I've seen this before)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for size that I've seen before include "Magnitude; glue" , "Physical magnitude" , "Dimensions, magnitude" , "stiffener" , "gelatinous mixture" .)