Sharpen weak sounds (4)
I believe the answer is:
'sharpen' is the definition.
(I know that whet is a more specific form of the action sharpen)
'weak sounds' is the wordplay.
'weak' becomes 'w' (physics symbol as in W-boson).
'sounds' becomes 'het' (I can't explain this - if you can you should give a lot more credence to this answer).
Can you help me to learn more?
(Other definitions for whet that I've seen before include "Arouse" , "Sharpen the blade of (a tool/weapon)" , "Sharpen by rubbing" , "Stimulate (appetite)" , "Make keen" .)