n 1  :  the act or action of concentrating: as  a  :  a directing of the attention or of the mental faculties toward a single object  b  :  an increasing of strength (as of a solute or a gas in a mixture) or a purifying by partial or total removal of diluents, solvents, admixed gases, extraneous material, or waste (as by evaporation or diffusion)  2  :  a crude active principle of a vegetable esp. for pharmaceutical use in the form of a powder or resin  3  :  the relative content of a component (as dissolved or dispersed material) of a solution, mixture, or dispersion that may be expressed in percentage by weight or by volume, in parts per million, or in grams per liter .
 
   
 
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