Crossword Genius

Papal publication — something to beware of? (4)

Ross

I believe the answer is:

bull

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'papal publication' is the definition.
The answer and definition can be both related to communication as well as being singular nouns.
Perhaps there's a link between them I don't understand?

I don't understand how the remainder of the clue works.

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(Other definitions for bull that I've seen before include "Male whale" , "Male elephant, say" , "Slangy lies from an ox?" , "Dartboard's centre" , "Male charging" .)

I've seen this clue in The Times.
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