/hal"eez/ or, sometimes, /hay"leez/, n.
a comet with a period averaging 76 years. In this century it was visible to terrestrial observers just before and after reaching perihelion in 1910 and again in 1986.
[named after Edmund HALLEY, who first predicted its return]
Pronunciation. The common pronunciation for both the comet and the astronomer after whom it is named is /hal"ee/. This is the pronunciation usually recommended by astronomers. However, several variant spellings of the name, including Hailey, Haley, and Hawley, were used interchangeably during the astronomer's own time, a period when spellings even of proper names were not yet fixed, and corresponding pronunciations have survived. The pronunciation /hay"lee/ in particular remains associated with HALLEY'S COMET; it is less likely to be heard as a pronunciation of Edmund HALLEY.
Useful english dictionary. 2012.