Definition of "proto-" [pro•to-]

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

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "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."