reactant

noun

substance consumed by a chemical reaction or biological process

Wiktionary

noun

Etymology: Etymology tree English react Proto-Indo-European *-onts Latin -ns Latin -āns Old French -antbor. Proto-Indo-European *-onts Proto-Germanic *-ndz Proto-West Germanic *-andī Old English -ende Middle English -ant English -ant English reactant From react + -ant.

Any of the participants present at the start of a chemical reaction, specifically one that is consumed during the reaction.