double file

plural double files

1. A double line, especially, a queue two persons wide.

   The column marching in double file, the instructor commands: […]

   1864, United States War Department, The 1864 Field Artillery Tactics, Stackpole Books, published 2005, →ISBN, page 120

   2 more examples

   In marching by double file, four abreast, etc., elbows touch and no lagging should be allowed.

   1891, Nettie D. Kimberlin, in Annual Report of the Controller of the City of Detroit of the Receipts and Expenditures of the Corporation, The Smith Printing Co., page 30

   There are three double files of stalked glands, one along each leaf margin, roughly speaking, and two rows along the under leaf surface, […]

   1942, Francis Ernest Lloyd, The Carnivorous Plants, READ BOOKS (publisher, 2007), page 100