What word is synonymous with "solder" in terms of physical joining?

The correct choice associated with "solder," in the context of physically joining materials, is "stanch." The term "solder" refers to the process of joining together two or more metal pieces using a filler metal that has a lower melting point than that of the workpieces. Similarly, "stanch," while often used in the context of stopping the flow of something (like blood), can also imply making an entity whole or secure, which can be related to the idea of securely joining items together.

The other options do not capture this meaning. "Sophistry" refers to a clever but misleading argument, which is not about physical joining. "Stygian" relates to darkness or the underworld, and does not pertain to the concept of joining at all. Therefore, "stanch" is the most appropriate synonym in this scenario, reflecting the notion of securely connecting or joining.