What term is used for fastening two ropes together for greater strength and permanence?

The term used for fastening two ropes together for greater strength and permanence is "splice." Splicing involves intertwining the fibers of the two ropes to create a strong connection that can withstand tension and is often more durable than simply tying a knot. This technique is commonly used in various applications, including sailing and climbing, where the integrity of the connection is crucial. A properly executed splice can maintain the rope's overall strength and provide a seamless joint that minimizes wear and reduces the bulk associated with knots.

Knot may refer to looping or tying the ends of rope together, but it doesn’t inherently provide the level of strength and permanence that splicing does. Fasten is a general term and does not specifically define the process or technique used for creating a strong rope connection. Joint is more commonly associated with connecting two structural components rather than specifically with ropes. Therefore, "splice" is the most appropriate term for this context.