write up vs bulletin

write up and bulletin both are nouns.

Word	Noun	Adjective	Verb	Adverb
write up	Yes	No	Yes	No
bulletin	Yes	No	Yes	No

As nouns, bulletin is a hyponym of write up; that is, bulletin is a word with a more specific, narrower meaning than write up:

write up: a short account of the news
bulletin: a brief report (especially an official statement issued for immediate publication or broadcast)

Other hyponyms of write up include newsletter, newssheet, communique, despatch, dispatch, urban legend, exclusive, scoop.

write up (noun)	bulletin (noun)
a short account of the news	a brief report (especially an official statement issued for immediate publication or broadcast)

write up (verb)	bulletin (verb)
bring to public notice by writing, with praise or condemnation	make public by bulletin
put into writing; write in complete form