There is a button here called Bezier, which is not wrong, but I am used to CAD programs calling it a "spline"
However, right underneath it is a button called "pline" in the code it is called polygon. It does not make curved lines but the icon looks like it does.
Perhaps you could use the "Toggle" icon but without the mouse cursor here? However, that may make users think it is a regular polygon. A tool to accomplish that would be great as well and in the Command Context Toolbar it could ask how many sides.

There is a button here called Bezier, which is not wrong, but I am used to CAD programs calling it a "spline"
However, right underneath it is a button called "pline" in the code it is called polygon. It does not make curved lines but the icon looks like it does.
Perhaps you could use the "Toggle" icon but without the mouse cursor here? However, that may make users think it is a regular polygon. A tool to accomplish that would be great as well and in the Command Context Toolbar it could ask how many sides.