Reducer

n.	1.	One who, or that which, reduces.
	2.	(Mach.) A contrivance for reducing the dimensions of one part so as to fit it to another, as a reducing coupling, or a device for holding a drilling a chuck.
	3.	(Photog.) A reducing agent, either a developer or an agent for reducing density.
	4.	(Chem.) a reducing agent.

Noun	1.	reducer - 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 slackened silver Synonyms: reducing agent, reductant
	2.	reducer - pipefitting that joins two pipes of different diameter

chemical agent, deoxidise, deoxidize, hydrazine, reduce, reducing agent, reductant