Proto-Indo-European

[proh-toh-in-doh-yoo r-uh-pee-uh n] /ˈproʊ toʊˌɪn doʊˌyʊər əˈpi ən/
noun
1.
the unattested prehistoric parent language of the Indo-European languages; Indo-European.
adjective
2.
of or pertaining to Proto-Indo-European.
British Dictionary definitions for Proto-Indo-European

Proto-Indo-European

noun
1.
the prehistoric unrecorded language that was the ancestor of all Indo-European languages