Cow without tail? Nonsense (4)
I believe the answer is:
bull
'nonsense' is the definition.
(I've seen this before)
'cow without tail?' is the wordplay.
'cow' becomes 'bully' (both can mean to intimidate someone).
'without tail?' means to remove the last letter (I've seen 'without tail' mean this).
'bully' with its final letter removed is 'BULL'.
(Other definitions for bull that I've seen before include "One charging" , "Taurus in the Constellations" , "Dartboard centre" , "Papal document; farm animal" , "Male charging" .)