dark brown or black pigment found in animal bodies, 1832, Modern Latin, with chemical suffix -in (2); the first element is from Greek melas (genitive melanos) "black" (see melano-). Related: Melanism; melanistic.
word-forming element meaning "black," from Greek melano-, combining form of melas (genitive melanos) "black, dark, murky,"probably from a PIE root *melh-"black, of darkish color" (source also of Sanskrit malinah "dirty, stained, black," Lithuanian mėlynas"blue," Latin mulleus "reddish").
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Definitions of melanin from WordNet
insoluble pigments that account for the color of e.g. skin and scales and feathers;