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three-square

American  
[three-skwair] / ˈθriˈskwɛər /

adjective

  1. having an equilateral triangular cross section, as certain files.

three-square British  

adjective

  1. having a cross section that is an equilateral triangle

    a three-square file
"Collins English Dictionary — Complete & Unabridged" 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Etymology

Origin of three-square

1400–50; late Middle English thre square threefold, modeled on foursquare

Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023

Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.