late 14c., from Medieval Latin retina "the retina," probably from Vulgar Latin (tunica) *retina, literally "net-like tunic," on resemblance to the network of blood vessels at the back of the eye, and ultimately from Latin rete "net" (see reticulate (adj.)). The Vulgar Latin phrase might be Gerard of Cremona's 12c. translation of Arabic (tabaqa) shabakiyyah "netlike (layer)," itself probably a translation of Greek amphiblestroeides (khiton).
