Dropping argument, starting late (3)
I believe the answer is:
pat
'dropping' is the definition.
(eg a cow pat)
'argument starting late' is the wordplay.
'argument' becomes 'spat' (I've seen this before).
'starting late' means to remove the first letter (the word starts later than the beginning).
'spat' with its initial letter taken off is 'PAT'.
(Other definitions for pat that I've seen before include "Glib; touch affectionately" , "Light hand stroke" , "Slick; dab" , "Portion of butter" , "Touch with hand" .)