single file, in

in single file

In a line one person or one thing in width. The students lined up and walked in single file into the auditorium. Cyclists are reminded to please ride in single file on roads to avoid obstructing traffic.
See also: file, single
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.

single file, in

Also, in Indian file. Aligned one behind the other, as in We have to bike in single file here, or The children were told to march in Indian file. Both usages are associated with military formations; the first term was first recorded in 1670; the variant, alluding to the usual marching order of Native Americans, was first recorded in 1758.
See also: single
The American Heritage® Dictionary of Idioms by Christine Ammer. Copyright © 2003, 1997 by The Christine Ammer 1992 Trust. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
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