An Etymological Dictionary of Astronomy and Astrophysics

The hypothetical and typically extinct language which is believed to be the ancestor of a group of languages of the same family.
Historical linguistics uses comparative study of the languages of a family to reconstruct the ancestral language even though in most cases it was never recorded. Some examples are → Proto-Indo-European, Proto-Germanic, Proto-Romance, Proto-Sino-Tibetan, etc.

See also: → proto-; → language.