Nonsense in letter from Pope (4)
I believe the answer is:
bull
'nonsense' is the definition.
(I've seen this before)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for bull that I've seen before include "fifty on board" , "Taurus in the Constellations" , "Male whale" , "motion is > nonsense" , "rubbish" .)