Emily Dickinson Lexicon

HE-LI'AC-AL, a. [L. heliacus; Fr. heliaque; from Gr. ἡλιος, the sun; W. haul.]

Emerging from the light of the sun, or passing into it. The heliacal rising of a star, is when, after being in conjunction with it and invisible, it emerges from the light so as to be visible in the morning before sun-rising. On the contrary, the heliacal setting of a star, is when the sun approaches so near as to render it invisible by its superior splendor. Encyc.