[hi-lahy-uh-kuh l]
adjective Astronomy.
  1. pertaining to or occurring near the sun, especially applied to such risings and settings of a star as are most nearly coincident with those of the sun while yet visible.
Also he·li·ac [hee-lee-ak] /ˈhi liˌæk/.

Origin of heliacal

1600–10; < Late Latin hēliac(us) (< Greek hēliakós; see heli-1, -ac) + -al1
Related formshe·li·a·cal·ly, adverb
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

Word Origin and History for heliac



"pertaining to the sun," c.1600, with -al (1) and Greek heliakos "of the sun," from helios "sun" (see sol). The heliacal year is reckoned from the heliacal rising of Sirius; thus it also is known as the canicular year.

Online Etymology Dictionary, © 2010 Douglas Harper