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porphyropsin

British  
/ ˌpɔːfɪˈrɒpsɪn /

noun

  1. a purple pigment occurring in the retina of the eye of certain freshwater fishes

"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

Etymology

Origin of porphyropsin

C20: from Greek porphura purple + -opsis + -in , on the model of rhodopsin