From HomoExcelsior

1. A small, light-sensitive patch of pigment in certain algae and unicellular organisms. 2. A simple visual organ of certain invertebrates consisting of a sensory ending covered by light-sensitive, pigmented cells. 3. A rounded eyelike marking, as on the tail of a peacock. 4. Either of two fungal diseases that affect grasses and are characterized by oval lesions.

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