2. The result of reducing: a reduction in absenteeism.
3. The amount by which something is lessened or diminished: a reduction of 12 percent in violent crime.
4. Biology The first meiotic division, in which the chromosome number is reduced. Also called reduction division.
5. Chemistry
a. A decrease in positive valence or an increase in negative valence by the gaining of electrons.
b. A reaction in which hydrogen is combined with a compound.
c. A reaction in which oxygen is removed from a compound.
6. Mathematics
a. The canceling of common factors in the numerator and denominator of a fraction.
b. The converting of a fraction to its decimal equivalent.
c. The converting of an expression or equation to its simplest form.
[Middle English reduccion, restoration, from Old French reduction, from Latin reducti, reductin-, from reductus, past participle of redcere, to bring back; see reduce.]
re·duction·al adj.
reduction[rɪˈdʌkʃən]
n
1. the act or process or an instance of reducing
2. the state or condition of being reduced
3. the amount by which something is reduced
4. a form of an original resulting from a reducing process, such as a copy on a smaller scale
5. a simplified form, such as an orchestral score arranged for piano
6. (Mathematics) Maths
a. the process of converting a fraction into its decimal form
b. the process of dividing out the common factors in the numerator and denominator of a fraction; cancellation
reductiveadj
reduction(r-dkshn)
1. The changing of a fraction into a simpler form, especially by dividing the numerator and denominator by a common factor. For example, the fraction 8/12 can be reduced to 4/6 , which can be further reduced to 2/3 , in each case by dividing both the numerator and denominator by 2.
2. A chemical reaction in which an atom or ion gains electrons, thus undergoing a decrease in valence. If an iron atom having a valence of +3 gains an electron, the valence decreases to +2. Compare oxidation.
Usage Beginning students of chemistry are understandably puzzled by the term reduction: shouldnt a reduced atom or ion be one that loses electrons rather than gains them? The reason for the apparent contradiction comes from the early days of chemistry, where reduction and its counterpart, oxidation, were terms invented to describe reactions in which one substance lost an oxygen atom and the other substance gained it. In a reaction such as that between two molecules of hydrogen (2H2) and one of oxygen (O2) combining to produce two molecules of water (2H2O), the hydrogen atoms have gained oxygen atoms and were said to have become oxidized, while the oxygen atoms have (as it were) lost them by attaching themselves to the hydrogens, and were said to have become reduced. Importantly, though, in the process of gaining an oxygen atom, the hydrogen atoms have had to give up their electrons and share them with the oxygen atoms, while the oxygen atoms have gained electrons. Thus comes the apparent paradox that the reduced oxygen has in fact gained something, namely electrons. Today the terms oxidation and reduction are used of any reaction, not just one involving oxygen, where electrons are (respectively) lost or gained.
reduction /rdkn/ n. [C;U] 1 a decrease, less of s.t.: A reduction of 100 employees was made after the company was sold.2 a decrease in price: This weekend, there is a 30% reduction on all shoes at that store.
d
k
n/ n. [C;U] 1 a decrease, less of s.t.: A reduction of 100 employees was made after the company was sold. 2 a decrease in price: This weekend, there is a 30% reduction on all shoes at that store. 
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k
sh
n)
, reducti
cere, to bring back; see reduce.]