When one object in space blocks the light from another, like when the Moon passes in front of the Sun, or when something becomes hidden or less important than something else.
From Greek 'ekleipsis' meaning 'abandonment' or 'failure to appear,' from 'ekleipein' (to leave out, fail). Ancient people thought the Sun or Moon was literally 'abandoning' us during an eclipse.
Ancient people were terrified of eclipses because they thought the Sun or Moon was being destroyed or attacked—but what's amazing is that the Greeks figured out the geometry well enough to predict them using cycles! An eclipse is literally perfect geometry: the Moon is about 400 times smaller than the Sun but 400 times closer, so they fit perfectly.
Complete word intelligence in one call. Free tier — 50 lookups/day.