c. 1400, from Late Latin triangularis "triangular, pertaining to a triangle," from Latin triangulus "with three corners" (the usual adjective in classical Latin), as a noun, "a triangle;" see triangle. Related: Triangularly.
In the huts of witches all the instruments and implements are triangular. ["Handwörterbuch des deutschen Aberglaubens"]
updated on September 25, 2018