An Etymological Dictionary of Astronomy and Astrophysics
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The abundance of a chemical element being lower than a reference value, in particular compared to that of the Sun.

→ under-; → abundance.

The region on the sky covered by the plane of the → Milky Way. It is characterized by an apparent absence of galaxies, due to the obscuring effect of → interstellar dust in the → Galactic plane.

→ zone; → avoidance.