reactant
reactant
Noun
pl: reactants
This term is used exclusively within the domain of chemistry to describe the starting materials of a chemical process. It carries a technical, precise connotation, focusing on the consumption of the substance as it transforms into a product. While often used interchangeably with reagent, a reactant is specifically any substance consumed in a reaction, whereas a reagent is typically a substance added to a system to cause a reaction or to test for the presence of another substance.