- 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.
- indicating the first in time, order, or rank
- primitive, ancestral, or original
- indicating the reconstructed earliest stage of a language
- indicating the first in a series of chemical compounds
- indicating the parent of a chemical compound or an element
