dateline vs date line

dateline and date line both are nouns.

Word	Noun	Adjective	Verb	Adverb
dateline	Yes	No	Yes	No
date line	Yes	No	No	No

As nouns, dateline and date line are synonyms defined as:

dateline and date line: an imaginary line on the surface of the earth following (approximately) the 180th meridian

Other synonyms of dateline include International Date Line.

dateline (noun)	date line (noun)
a line at the beginning of a news article giving the date and place of origin of the news dispatch	an imaginary line on the surface of the earth following (approximately) the 180th meridian
an imaginary line on the surface of the earth following (approximately) the 180th meridian

dateline (verb)	date line (verb)
mark with a date and place