n.1. A logical or natural association between two or more things; relevance of one to another; connection: the relation between smoking and heart disease.
2. The connection of people by blood or marriage; kinship.
3. A person connected to another by blood or marriage; a relative.
4. The way in which one person or thing is connected with another: the relation of parent to child.
5. relationsa. The mutual dealings or connections of persons, groups, or nations in social, business, or diplomatic matters: international relations.
b. Sexual intercourse.
6. a. The act of telling or narrating.
b. A narrative; an account.
7. Mathematics A correspondence between two sets, consisting of a set of ordered pairs, the first element of each of which is from the first set, and the second element of each of which is from the second set. If A = {1,2} and B = {3,4}, then {(1,3), (1,4)} is a relation from A to B.
8. Law The principle by which an action done on a certain date is treated as having been done on an earlier date. Also called relation back.