a line at the beginning of a newspaper article or letter that shows the date and place where the story was written.
Combination of 'date' (from Latin 'data' meaning 'given') and 'line' (from Old English 'līne'). The term emerged in journalism during the 19th century as newspapers needed to indicate when and where stories originated.
The International Date Line is a completely different thing—it's an invisible boundary on Earth where the calendar date changes by a full day! But dateline in journalism is just telling readers 'this story was written in Chicago on March 5th' so they know how fresh the news is.
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