Dictionary.com
definitions

Proto-Indo-European

[proh-toh-in-doh-yoo r-uh-pee-uh n]
noun
  1. the unattested prehistoric parent language of the Indo-European languages; Indo-European.
adjective
  1. of or relating to Proto-Indo-European.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018
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
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012