eyespot

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. Botany. Either of two fungal diseases that affect grasses and are characterized by oval lesions.

The noun has one meaning:

Meaning #1: an eyelike marking (as on the wings of some butterflies); usually a spot of color inside a ring of another color
  Synonym: ocellus