n.
Variant: or proto-
Function: combining form
Etymology: Greek pr ō t-, pr ō to-, from pr ō tos; akin to Greek pro before ― more at FOR
1 a : first in time < proto history> b : beginning : giving rise to < proto planet>
2 : parent substance of a (specified) substance < prot actinium>
3 : first formed : primary < proto xylem>
4 capitalized : relating to or constituting the recorded or assumed language that is ancestral to a language or to a group of related languages or dialects < Proto- Indo-European>