I don't have a dog in this fight, and anyway dogfighting is bad, but the intro to the Wikipedia article[0] reads:

> An operating system shell is a computer program that provides relatively broad and direct access to the system on which it runs. The term shell refers to how it is a relatively thin layer around an operating system.

> Most shells are command-line interface (CLI) programs. Some graphical user interfaces (GUI) also include shells.

The last line I think supports the notion that the term "shell" at least implies a CLI, but I can understand both positions.

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0. https://en.wikipedia.org/wiki/Shell_(computing)

Edit: I'm shite at formatting on HN