1.  ocellus(n = noun.body) simple eye, stemma - an eye having a single lens;
is a kind of eye, oculus, optic
has particulars: ommatidium

2.  ocellus(n = noun.attribute) eyespot - an eyelike marking (as on the wings of some butterflies); usually a spot of color inside a ring of another color;
is a kind of marking

   A little eye; a minute simple eye found in many invertebrates. [1913 Webster]

ocellus, n. (pl. ocelli)
1 each of the simple, as opposed to compound, eyes of insects etc.
2 a spot of colour surrounded by a ring of a different colour on the wing of a butterfly etc.

Derivative:
ocellar adj. ocellate adj. ocellated adj.

Etymology:
L, dimin. of oculus eye