I feel down a rabbit hole, a few years ago wonder the same thing about C#. Here is what I found.
- C# was developed in 2000 as a successor to C++. Doubling the ++ to a #.
- C++ was developed in the early 80s as a successor to C. Adding plus (+) to a name was a common way of indicating it was an enhancement. Also ++ is the incrementing operator for C.
- C was developed in the early 70s as a successor to the B programming language. C comes after B.
- B was developed in 1969 and was derived from the BCPL language. Basically, B was a stripped down version of BCPL.
- BCPL (Basic Combined Programming Language) was developed in 1967 and was a designed as an simpler version of CPL.
- CPL (Combined Programming Language) was developed in the early 60s at Cambridge. The original name was "Cambridge Programming Language" but was changed to Combined when it was published jointly with the University of London.