The Collaborative International Dictionary of English v.0.48:
Halo \Ha"lo\ (h[=a]"l[-o]), n.; pl. Halos (-l[=o]z). [L.
halos, acc. halo, Gr. "a`lws a thrashing floor, also (from
its round shape) the disk of the sun or moon, and later a
halo round it; cf. Gr. e'ily`ein to enfold, 'ely`ein to roll
round, L. volvere, and E. voluble.]
1. A luminous circle, usually prismatically colored, round
the sun or moon, and supposed to be caused by the
refraction of light through crystals of ice in the
atmosphere. Connected with halos there are often white
bands, crosses, or arches, resulting from the same
2. A circle of light; especially, the bright ring represented
in painting as surrounding the heads of saints and other
holy persons; a glory; a nimbus.
3. An ideal glory investing, or affecting one's perception
of, an object.
4. A colored circle around a nipple; an areola.