Punch black and blue (4)
I believe the answer is:
blow
'punch' is the definition.
(thesaurus)
'black and blue' is the wordplay.
'black' becomes 'b' (as in pencil classifications).
'and' means one lot of letters go next to another.
'blue' becomes 'low' (both can mean sad).
'b'+'low'='BLOW'
(Other definitions for blow that I've seen before include "Shock; sound (a horn)" , "Hit - disappointment" , "Bang, wallop" , "Be windy; unlucky stroke" , "Use pipe for" .)