he·​li·​a·​cal hi-ˈlī-ə-kəl How to pronounce heliacal (audio)
: relating to or near the sun
used especially of the last setting of a star before and its first rising after invisibility due to conjunction with the sun
heliacally adverb

Did you know?

The word heliacal rose in the mid-16th century. Its source is the Greek word hēlios, meaning "sun." Helios is also the Sun god of ancient Greece. Heliacal often suggests a relationship between a star and the sun as they appear to the human eye in the sky. It is also used in reference to the ancient Egyptian year, which began on the date when Sirius (or the Dog Star) first appeared on the eastern horizon at sunrise. English speakers have referred to this year as the heliacal year or the Sothic year. (Sothic comes from "Sōthēs," the Greek word for Sirius.)

Example Sentences

Recent Examples on the Web The Babylonians of the first millennium B.C. recorded their astronomical knowledge in a similar way, by inscribing on clay tablets the heliacal rising of important stars — that is, the day that a star first appears above the horizon each year. Cody Cottier, Discover Magazine, 13 Jan. 2023 There are lots of celestial bodies, but the biggest is Sirius, the dog star, and the 20 days before and the 20 days after its heliacal rising are called the dog days. Kevin Fisher-paulson, SFChronicle.com, 10 July 2018

These examples are programmatically compiled from various online sources to illustrate current usage of the word 'heliacal.' Any opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback about these examples.

Word History


Late Latin heliacus, from Greek hēliakos, from hēlios

First Known Use

1545, in the meaning defined above

Time Traveler
The first known use of heliacal was in 1545


Dictionary Entries Near heliacal

Cite this Entry

“Heliacal.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/heliacal. Accessed 6 Jun. 2023.

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