'Reducing agent' definitions:

Definition of 'reducing agent'

(from WordNet)
noun
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: reducing agent, reducer, reductant]

Definition of 'Reducing agent'

From: GCIDE
  • Reducing agent \Re*du"cing a`gent\, 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]