news bulletin vs bulletin

news bulletin and bulletin both are nouns.

Word	Noun	Adjective	Verb	Adverb
news bulletin	Yes	No	No	No
bulletin	Yes	No	Yes	No

As nouns, bulletin is a hypernym of news bulletin; that is, bulletin is a word with a broader meaning than news bulletin:

news bulletin: a short news announcement concerning some on-going news story
bulletin: a brief report (especially an official statement issued for immediate publication or broadcast)

news bulletin (noun)	bulletin (noun)
a short news announcement concerning some on-going news story	a brief report (especially an official statement issued for immediate publication or broadcast)

news bulletin (verb)	bulletin (verb)
	make public by bulletin