o·cel·lus 
(ō-sĕləs)
(ō-sĕləs)n. pl. o·cel·li (ō-sĕlī′)
1. A simple eye, found in many invertebrates, consisting of a number of sensory cells and often a single lens.
2. A marking that resembles an eye, as on the tail feathers of a male peacock; an eyespot.
[Latin, diminutive of oculus, eye; see okw- in the Appendix of Indo-European roots.]
o·cellar (ō-sĕlər) adj.
ocelluspeacock feather