from The American Heritage® Dictionary of the English Language, 4th Edition

  • First in time; earliest: protolithic.
  • First formed; primitive; original: protohuman.
  • Being a form of a language that is the ancestor of a language or group of related languages: Proto-Germanic.
  • Having the least amount of a specified element or radical: protoporphyrin.

from Wiktionary, Creative Commons Attribution/Share-Alike License

  • first
  • Used to form the name of the hypothetical ancestor of a family of languages.

from the GNU version of the Collaborative International Dictionary of English

  • A combining form prefix signifying first, primary, primordial
  • Denoting the first or lowest of a series, or the one having the smallest amount of the element to the name of which it is prefixed; as protoxide, protochloride, etc.
  • Sometimes used as equivalent to mono-, as indicating that the compound has but one atom of the element to the name of which it is prefixed. Also used adjectively.

from The Century Dictionary and Cyclopedia

  • n. An element in compound words of Greek origin, meaning ‘first,’ and denoting precedence in time, rank, or degree.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

  • adj. indicating the first or earliest or original


Greek prōto-, from prōtos; see per1 in Indo-European roots.
(American Heritage® Dictionary of the English Language, Fourth Edition)
From Ancient Greek πρωτο- (proto-), combination form of πρῶτος (protos, "first"), superlative of πρό (pro, "before"). (Wiktionary)


  • Each of the proto-"Avengers'' movies ends with a post-credits teaser scene that advances the meta-narrative; the one in "Thor'' had the fan-guy sitting next to me reeling in shock. Top Stories


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