1. 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-.

Origin of proto-

< Greek, combining form representing prôtos first, superlative formed from pró; see pro-2 Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

Examples from the Web for proto

Contemporary Examples of proto

Historical Examples of proto

  • Preservation of antiquities, 22 f. 'Proto–Corinthian' pottery, 41.

  • The ferrous or proto salts have generally a greenish colour, but yield nearly colourless908 solutions, except when concentrated.

  • Ferricyanide of potassium deepens the colour, but does not give a blue precipitate, as it does with ferrous salts (proto salts).

  • The snakes show the same extraordinary activity on the proto level as on the gaseous, twisting and writhing, darting and coiling.

    Occult Chemistry

    Annie Besant and Charles W. Leadbeater

  • The funnels let go the globes, but the eight ovoids remain within them, so that seven bodies are let loose on the proto level.

    Occult Chemistry

    Annie Besant and Charles W. Leadbeater

British Dictionary definitions for proto


sometimes before a vowel prot-

combining form
  1. indicating the first in time, order, or rankprotomartyr
  2. primitive, ancestral, or originalprototype
  3. indicating the reconstructed earliest stage of a languageProto-Germanic
  4. indicating the first in a series of chemical compoundsprotoxide
  5. indicating the parent of a chemical compound or an elementprotactinium

Word Origin for proto-

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

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

proto in Medicine


  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.