What marlinespike seamanship term is used when two lines or two parts of a line are to be permanently married?

The term used when two lines or two parts of a line are to be permanently married is "splice." Splicing involves intertwining the fibers or ends of the lines in such a way that they form a strong, permanent connection. This technique provides a seamless join that maintains the strength and integrity of the rope, which is particularly important in maritime operations where reliability of lines is crucial.

In contrast, seizing refers to a method of securing a line or rope to another object or line, typically using smaller line or thread, but it does not involve permanently joining two lines. Whipping is a technique used to prevent the fraying of the end of a rope or line, typically by binding the ends with twine or thread. Securing is a broader term that can imply various methods of tying or binding lines and does not specifically address the permanent joining of two separate lines.