a reaction between two substances in which two parts of each substance are exchanged; metathesis
Example AgNO3 + NaCl => AgCl + NaNO3.
A chemical reaction between two compounds in which the first and second parts of one reactant are united, respectively, with the second and first parts of the other reactant
a chemical reaction between two compounds in which parts of each are interchanged to form two new compounds (AB+CD=AD+CB)