Is border a synonym of rule?

No, "border" and "rule" are not synonyms. They have distinct meanings:

* Border: A line separating two countries, states, or areas. It can also refer to the edge or outer limit of something.

* Rule: A principle or regulation that governs conduct or procedure.

Here are some examples to illustrate the difference:

* Border: "The border between Mexico and the United States is heavily guarded."

* Rule: "The rule of law states that everyone is equal before the court."

While they might be used in similar contexts (e.g., talking about the law), they refer to fundamentally different concepts.