/mul"euhr luy"euhr, myooh"leuhr-, mil"euhr-/ ; Ger. /myuul"euhrdd lee"euhrdd/
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.
[ after Franz-Karl Müller-Lyer (1857-1916), German sociologist, who described the illusion in 1889 ]