say it: DAYT-lahyn
dateline is a noun and verb meaning "an imaginary line on the surface of the earth following (approximately) the 180th meridian". It carries 3 recorded senses.
an imaginary line on the surface of the earth following (approximately) the 180th meridian
Forms marked · are formed by the regular rule rather than recorded in the source data. English keeps a few hundred irregulars and the rest follow the pattern, so the rule is right far more often than not — but it is a rule, and the mark says so.
Definitions, synonyms and semantic relations for dateline come from Princeton University’s WordNet. The pronunciation comes from the CMU Pronouncing Dictionary. Commonness is measured against a corpus of everyday English. Full sources and licences.