On Black Friday, the day after Thanksgiving, Americans kick off the holiday shopping season with a bang. In his Word Routes column last year, lexicographer Ben Zimmer explored the origins of the phrase "Black Friday." It is not, as many believe, the day when retailers' balance sheets change from red to black.

The latest research on the origins of "Black Friday" has been conducted by Bonnie Taylor-Blake, who has shared her findings on the mailing list of the American Dialect Society. The earliest known example of "Black Friday" to refer to the day after Thanksgiving is from an article entitled "Friday After Thanksgiving" in the November 1951 issue of Factory Management and Maintenance. The article (posted by Taylor-Blake here) was about worker absenteeism on that day, rather than the shopping rush.

But in the early 1960s, "Black Friday" came to be used in Philadelphia to describe the post-Thanksgiving shopping rush. Taylor-Blake discovered an article in a public relations newsletter from 1961 that uses "Black Friday" in its current meaning.

The origin of "Black Friday" among Philadelphia police officers of the early '60s is further reinforced by a 1994 article for The Philadelphia Inquirer by Joseph P. Barrett, who recounted his role in popularizing the expression when he worked as a reporter for The Philadelphia Bulletin. He credits the traffic cops, who had to work 12-hour shifts the day after Thanksgiving.

Read the whole column here, and listen to more from Ben Zimmer on WBUR's Radio Boston.