Proto-Indo European
— Noun
– English
～ a prehistoric unrecorded language that was the ancestor of all Indo-European languages
proto-oncogene
— Noun
– English
～ a normal gene that has the potential to become an oncogene
Proto-Norse
— Noun
– English
～ the Germanic language of Scandinavia up until about 700
proto
— Adjective
– English
～ indicating the first or earliest or original; "`proto' is a combining form in a word like `protolanguage' that refers to the hypothetical ancestor of another language or group of languages"