1. noun /ˈheɪləʊ/ˈheɪɫoʊ
a) A circular band of coloured light, visible around the sun or moon etc., caused by reflection and refraction of light by ice crystals in the atmosphere.
b) A cloud of gas and other matter surrounding and captured by the gravitational field of a large diffuse astronomical object, such as a galaxy or cluster of galaxies.
2. verb /ˈheɪləʊ/ˈheɪɫoʊ
To encircle with a halo.
See Also: halation
Wikipedia foundation.