deduction (dɪˈdʌkʃən)  
—n  
1.  the act or process of deducting or subtracting 
2.  something, esp a sum of money, that is or may be deducted 
3.  a. the process of reasoning typical of mathematics and logic, whose conclusions follow necessarily from their premises 
b. an argument of this type  
c. the conclusion of such an argument  
4.  logic 
a. a systematic method of deriving conclusions that cannot be false when the premises are true, esp one amenable to formalization and study by the science of logic  
b. Compare induction an argument of this type 
deduction (dĭdŭk'shən) Pronunciation Key
Our Living Language : The logical processes known as deduction and induction work in opposite ways. In deduction general principles are applied to specific instances. Thus, using a mathematical formula to figure the volume of air that can be contained in a gymnasium is applying deduction. Similarly, applying a law of physics to predict the outcome of an experiment is reasoning by deduction. By contrast, induction makes generalizations based on a number of specific instances. The observation of hundreds of examples in which a certain chemical kills plants might prompt the inductive conclusion that the chemical is toxic to all plants. Inductive generalizations are often revised as more examples are studied and more facts are known. If certain plants that have not been tested turn out to be unaffected by the chemical, the conclusion about the chemical's toxicity must be revised or restricted. In this way, an inductive generalization is much like a hypothesis. 
A process of reasoning that moves from the general to the specific. (Compare induction.)
deduction definition
