triangle Look up triangle at Dictionary.com
late 14c., from O.Fr. triangle (13c.), from L. triangulum "triangle," from neut. of adj. triangulus "three-cornered," from tri- "three" + angulus "corner, angle." Triangulation is recorded from 1818.
"In the huts of witches all the instruments and implements are triangular." ["Handwörterbuch des deutschen Aberglaubens"]