/ri dooh"seuhr, -dyooh"-/ , n.
1. a person or thing that reduces.
2. Photog.
a. an oxidizing solution for lessening the density of an exposed negative.
b. a developing agent.
3. (in plumbing) a coupling decreasing in diameter at one end. Cf. increaser (def. 2).
[ 1520-30; REDUCE + -ER 1 ]