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. 2019

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 central globe shows a cross at its centre, with the four quintets whirling round it, on the proto level.

    Occult Chemistry

    Annie Besant and Charles W. Leadbeater

  • In yttrium, on the proto level, a 110 and b 63 both escape from the funnel, and behave as in scandium.

    Occult Chemistry

    Annie Besant and Charles W. Leadbeater

British Dictionary definitions for proto


sometimes before a vowel prot-

combining form

indicating the first in time, order, or rankprotomartyr
primitive, ancestral, or originalprototype
indicating the reconstructed earliest stage of a languageProto-Germanic
indicating the first in a series of chemical compoundsprotoxide
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



First in time:prototype.
First formed; primitive; original:protoplast.
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.