tapetum lucidum
noun
tapetum lu·ci·dum
| \ -ˈlü-si-dəm
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Medical Definition of tapetum lucidum
: a layer in the choroid chiefly of nocturnal mammals that reflects light causing the eyes to glow when light strikes them at night and that is made up of several layers of flattened cells covered by a zone of doubly refracting crystals