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Webster 1913 Edition

(-s?r)

Noun.

One who, or that which, reduces.

Noun.

One that reduces.

reducer ‎(plural reducers)

Something that reduces.
(photography) A liquid used in the process of developing a negative to reduce its darkness.
(plumbing) A component used to connect two pipes of different bores.
A hydraulic device for reducing pressure and hence increasing movement, used to transmit the load from the hydraulic support of the lower shackle to the lever weighing apparatus in some kinds of heavy testing machine.

something that reduces

photography: developing liquid

plumbing component