before vowels prot-, word-forming element meaning "first, source, parent, preceding, earliest form, original, basic," from Greek prōto-, from prōtos "first," from PIE *pre-, from root *per- (1) "forward" (hence "before, first").
Proteus
prothalamion
prothesis
prothonotary
protist
proto-
protocol
Proto-Indo-European
proto-language
proton
protoplanet