1the action or fact of making something smaller or less in amount, degree, or size:talks on arms reduction [count noun]:there had been a reduction in the number of casualties
[count noun] the amount by which something is made smaller, less, or lower in price:special reductions on knitwear
the simplification of a subject or problem to a particular form in presentation or analysis:the reduction of classical genetics to molecular biology
Mathematics the process of converting an amount from one denomination to a smaller one, or of bringing down a fraction to its lowest terms.
Biology the halving of the number of chromosomes per cell that occurs at one of the two anaphases of meiosis.
2 [count noun] a thing that is made smaller or less in size or amount, in particular:
an arrangement of an orchestral score for piano or for a smaller group of performers.
a thick and concentrated liquid or sauce made by boiling.
a copy of a picture or photograph made on a smaller scale than the original.
3the action of remedying a dislocation or fracture by returning the affected part of the body to its normal position:we must see if the fracture requires reduction
4 Chemistry the process or result of reducing or being reduced:the reaction is limited to reduction to the hydrocarbon
5 Phonetics substitution of a sound which requires less muscular effort to articulate:the process of vowel reduction
late Middle English (denoting the action of bringing back): from Old French, or from Latin reductio(n-), from reducere 'bring back, restore' (see reduce). The sense development was broadly similar to that of reduce; sense 1 dates from the late 17th century
reduction in other Oxford dictionaries
Definition of reduction in the US English dictionary