I've seen pronunciation guides and all sorts of definitions of .NET as a framework, but no definition or explanation of the actual name of the framework.
Wikipedia doesn't seem to know. This question didn't cover it.
Anybody know? Is it pure marketing-generated nonsense, or does it mean something?
It's not an acronym.
In the beginning - around 1997 - there was Project Lightning. It was also known as Project 42 because DevDiv (Microsoft's Developer Division) lived (and still lives) in Building 42 on the Redmond Campus. (I've always thought that was an awesome building number for DevDiv with the little hat tip to Douglas Adams' Hitchhikers Guide to the Galaxy. I've always wondered if it was intentional.) Early press announcements referred to it as "Next Generation Windows Services". Eventually Project Lightning was dubbed Microsoft .NET, though some code names have been forever baked into the system.
Marketing was thinking of calling it COM+ 2.0 or the Universal Runtime (URT). Another idea was the COM Object Runtime (COR). Hence mscorlib.dll, which is still the assembly that holds the CLR's main types and is the one assembly that must be loaded in every .NET app domain. (System.dll is often loaded, but need not be. Mscorlib.dll contains the code for System.String, System.Int32, etc. You honestly can't do anything without mscorlib.dll loaded.)