As nouns the difference between hi and halo
is that
hi is "Hi" or similar greeting while
halo is 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.
As an interjection hi
is a friendly, informal, casual greeting said when meeting someone.
As an adjective hi
is informal spelling of lang=en, often hyphenated.
As an abbreviation HI
is hawaii, a state of the United States of America.
As a verb halo is
to encircle with a halo.