In the cases where they are reasonably synonymous, relationship tends to refer to people and also suggests (to me) a greater complexity of relations (definition #1)-- Quick definitions ( relation ) noun : an abstraction belonging to or characteristic of two entities or parts together noun : (usually plural) mutual dealings or connections among persons or groups ( Example: "International relations" ) Quick definitions ( relationship ) noun : a relation between people; (`relationship' is often used where `relation' would serve, as in `the relationship between inflation and unemployment', but the preferred usage of `relationship' is for human relations or states of relatedness) ( Example: "The relationship between mothers and their children" ) noun : a state of connectedness between people (especially an emotional connection) ( Example: "He didn't want his wife to know of the relationship" ) noun : a state involving mutual dealings between people or parties or countries
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