1. communication by exchange of letters; correspondence
Usage: somewhat formal or archaic; 'correspondence' is the more common modern term
2. agreement or harmony between things; a relationship of similarity or connection
Usage: formal; often used in philosophical or technical contexts

Examples

• The correspondency between the two scholars lasted for decades through their letters.
• There is a clear correspondency between the structure of the novel and the author's life experiences.
• The correspondency of the data with the theoretical predictions was remarkable.
• She maintained an active correspondency with friends abroad.
• The correspondency between supply and demand determines market prices.