The word “tonk” does not have a clear origin. Some say it’s an acronym for some variation of “Traveler, Origin Not Known” or “Traveler Outside Native Country.”

The broadest consensus among those familiar with it, however, is that the slur comes from the sound made by slamming a heavy-duty flashlight or baton over a migrant’s head.

Though no one can say for sure, the flashlight definition has adherents within the agency. In an email with the subject line “Tonk,” a Border Patrol agent in the Spokane, Washington, region asked whether someone ”‘found’ that head wound with his maglite.” (The names in the documents released to HuffPost were redacted.)