Sharpen the damaged point first (4)
I believe the answer is:
'sharpen' is the definition.
(whetting is a kind of sharpening)
'the damaged point first' is the wordplay.
'damaged' indicates anagramming the letters.
'point' becomes 'w' (W is an example**).
'first' says to put letters next to each other.
'the' with letters rearranged gives 'het'.
'het' after 'w' is 'WHET'.
(Other definitions for whet that I've seen before include "'Sharpen, appetite say (4)'" , "Sharpen by grinding" , "Excite" , "Sharpen - stimulate" , "Sharpen the blade of (a tool/weapon)" .)