Definition from Wiktionary, the free dictionary
Proper noun 
- (linguistics, uncountable) The hypothetical ancestor language or protolanguage of the Indo-European family of languages, which includes most European and Indian languages.
- (anthropology, countable) A person who spoke the Proto-Indo-European language.
- (dated) Proto-Indo-Germanic
See also 
Proto-Indo-European is the hypothetical ancestor language of many languages, including the following major groups:
- Wiktionary:About Proto-Indo-European
- Wiktionary Appendix:List of Proto-Indo-European roots
- Appendix:Proto-Indo-European Swadesh list for a Swadesh list of basic vocabulary words in Proto-Indo-European
ancestor language of most European and Indian languages
person who spoke the Proto-Indo-European language
Proto-Indo-European (not comparable)
- (linguistics, anthropology) Of or pertaining to the Proto-Indo-European language, or the people who spoke it.
pertaining to the Proto-Indo-European language, or the people who spoke it