proto-

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.

proto-

combining form

1. indicating the first in time, order, or rank

   protomartyr

2. primitive, ancestral, or original

   prototype

3. indicating the reconstructed earliest stage of a language

   Proto-Germanic

4. indicating the first in a series of chemical compounds

   protoxide

5. indicating the parent of a chemical compound or an element

   protactinium

Word History and Origins

Origin of proto-¹

< Greek, combining form representing prôtos first, superlative formed from pró; pro- ²

Word History and Origins

Origin of proto-¹

from Greek prōtos first, from pro before; see _pro- ²

Example Sentences

Researchers from MIT and collaborating institutions have uncovered exceptionally rare traces of "proto Earth," the ancient precursor to our planet that existed about 4.5 billion years ago.

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These meteorites gradually merged through repeated impacts to create the proto Earth and its neighboring planets.

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For decades, scientists believed that any trace of the proto Earth had been completely destroyed in that cosmic upheaval.

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The most plausible explanation is that these rocks preserve tiny portions of the proto Earth's original material, somehow surviving the planet's violent reshaping.

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"This is maybe the first direct evidence that we've preserved the proto Earth materials," says Nicole Nie, the Paul M. Cook Career Development Assistant Professor of Earth and Planetary Sciences at MIT.

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When To Use

What does proto- mean?

Proto- is a combining form used like a prefix meaning “first,” "foremost,” or “earliest form of.” In terms from chemistry, it specifically denotes the first in a series of compounds or the compound containing the minimum amount of an element. It is often used in scientific and technical terms, especially in biology.Proto- comes from Greek prôtos, meaning “first.” The word proton, meaning "a positively charged elementary particle," ultimately shares this same Greek root. The Latin cognate of prôtos is prīmus “first,” which is the source of primary and prime. Check out our entries for both words to learn more.What are variants of proto-?When combined with words or word elements that begin with a vowel, proto- becomes prot-, as in protium. Want to know more? Read our Words That Use prot- article.