This word is acceptable for play in the US & UK dictionaries that are being used in the following games:

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n. Any of a group of naturally occurring dark pigments, especially the pigment found in skin, hair, fur, and feathers.

n. Any of a group of naturally occurring dark pigments, especially the pigment found in skin, hair, fur, and feathers.

n. A black pigment found in the pigment-bearing cells of the skin (particularly in the skin of the negro), in the epithelial cells of the external layer of the retina (then called fuscin), in the outer layer of the choroid, and elsewhere. It is supposed to be derived from the decomposition of hemoglobin.

n. The black pigment of the hair, choroid, retina, and epidermis of colored races; also, the dark pigment seen in melanæmia and in melanosarcoma and melanocarcinoma. The pigments in these cases may, however, be different.

n. insoluble pigments that account for the color of e.g. skin and scales and feathers

"What determines how much melanin is present in the iris ishereditary genetics."

animal pigment   

fuscin   

solid-rocket    phosphene    primary-response    thousand-ton    solid-fueled    retrievable    heavy-lift    light-speed    anthocyanin    strap-on