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

Seizing is the correct answer because it refers to the method of securing two lines or two parts of a single line together in a permanent manner, often by wrapping a smaller line around the two being joined. This technique is particularly useful for ensuring that the lines remain bound together and can withstand the tension or load applied to them over time.

In contrast, coxcombing involves the decorative process of tying small knots or patterns at intervals along a line, but it does not serve the purpose of permanently joining two lines. Marlinspike typically refers to tools or techniques used for working with rope or line, but does not specifically address the act of joining lines. Knotting is a general term that describes various techniques to tie knots in lines, but many knots are not suitable for permanent marriage of lines, as they may be designed for temporary use or allow for easy untying.