Müller-Lyer illusion

[ muhl-er-lahy-er, myoo-ler-, mil-er-; German myl-uh r-lee-uh r ]
/ ˈmʌl ərˈlaɪ ər, ˈmyu lər-, ˈmɪl ər-; German ˈmül ərˈli ər /

noun

a geometric illusion in which two lines of equal length appear unequal depending on whether angular lines forming arrowheads at each end point toward or away from each other.

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Origin of Müller-Lyer illusion

after Franz-Karl Müller-Lyer (1857–1916), German sociologist, who described the illusion in 1889
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2020

British Dictionary definitions for muller-lyer illusion

Müller-Lyer illusion
/ (ˈmuːləˈlaɪə) /

noun

an optical illusion in which a line with inward pointing arrowheads is seen as longer than an equal line with outward pointing arrowheads

Word Origin for Müller-Lyer illusion

C19: named after Franz Müller-Lyer (1857–1916), German sociologist and psychiatrist
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