news article vs sidebar

news article and sidebar both are nouns.

Word	Noun	Adjective	Verb	Adverb
news article	Yes	No	No	No
sidebar	Yes	No	No	No

As nouns, sidebar is a hyponym of news article; that is, sidebar is a word with a more specific, narrower meaning than news article:

Other hyponyms of news article include lead, lead story, personal.

news article (noun)	sidebar (noun)
an article reporting news	(law) a courtroom conference between the lawyers and the judge that is held out of the jury's hearing
	a short news story presenting sidelights on a major story