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a combining form meaning “first,” “foremost,” “earliest form of,” used in the formation of compound words (protomartyr; protolithic; protoplasm), specialized in chemical terminology to denote the first of a series of compounds, or the one containing the minimum amount of an element.
Also, especially before a vowel, prot-.
< Greek, combining form representing prôtos first, superlative formed from pró; see pro-2 Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2015.
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Examples from the web for proto
  • proto-snakes might have burrowed underground searching for food in small crevices.
  • These changes were probably in response to the arrival of new prey as other reptiles, the proto-birds, took to the air.
  • The proto-scientists did not spring into being as paid-up believers in modern materialism and rationality.
  • The first proto-dogs probably remained fairly isolated from each other for several thousand years.
  • Scrip of this kind becomes, in effect, a proto-currency.
  • Thus allowing developers to build production part data as they are testing the proto car.
  • Before this all but proto-historic transmogrification of the land-face.
  • But a kind of proto-journalism is emerging, and becoming steadily more sophisticated.
  • The two major camps have proto-birds either dropping from trees or running along the ground before finally taking to the air.
  • There are the beginnings of digits, proto-wrists, elbows and shoulders.
British Dictionary definitions for proto


combining form
indicating the first in time, order, or rank: protomartyr
primitive, ancestral, or original: prototype
indicating the reconstructed earliest stage of a language: Proto-Germanic
indicating the first in a series of chemical compounds: protoxide
indicating the parent of a chemical compound or an element: protactinium
Word Origin
from Greek prōtos first, from pro before; see pro-²
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
© William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
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Word Origin and History for proto


before vowels prot-, word-forming element meaning "first, source, parent, preceding, earliest form, original, basic," from Greek proto-, comb. form of protos "first," from PIE *pre-, from root *per- (1) "forward, through" (see per).

Online Etymology Dictionary, © 2010 Douglas Harper
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proto in Medicine

proto- or prot-

  1. First in time: prototype.

  2. First formed; primitive; original: protoplast.

  3. Having the least amount of a specified element or radical: protoporphyrin.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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