(1):

(n.) 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 atmospheric conditions.

(2):

(v. t. & i.) To form, or surround with, a halo; to encircle with, or as with, a halo.

(3):

(n.) 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.

(4):

(n.) A colored circle around a nipple; an areola.

(5):

(n.) An ideal glory investing, or affecting one's perception of, an object.