Definition of heliacal in English:

heliacal

adjective

Astronomy
  • Relating to or near the sun.

    • ‘All ancient astrologers placed the greatest significance upon heliacal risings and settings and ancient Mesopotamian astrology was also heavily predisposed to observance of this kind of planetary phenomena.’
    • ‘It is possible that all the planetary orbs originate from an early attempt to record heliacal obscurity.’
    • ‘The Greeks and Romans, with fairly useless calendars, continued to depend upon observing the heliacal risings and settings of stars.’

Origin

Mid 16th century: via late Latin from Greek hēliakos (from hēlios ‘sun’) + -al.

Pronunciation

heliacal

/həˈlīəkəl/