(n)a substance capable of bringing about the reduction of another substance as it itself is oxidized; used in photography to lessen the density of a negative or print by oxidizing some of the loose silver, Syn.reductant, reducer
The Collaborative International Dictionary of English (GCIDE) v.0.53Collaborative International Dictionary (GCIDE)
n. (Chem.) a substance that causes reduction of another substance in a chemical reaction, as by donating electrons or adding hydrogen atoms; as, lithium hydride is a powerful reducing agent. [ PJC ]