Explanation:

- Grumble: Correctly spelled. It means to complain about something in a bad-tempered way.

- Groove: Correctly spelled. It refers to a long, narrow cut or depression, especially one made to guide motion or receive a corresponding ridge.

- Grownd: Incorrectly spelled. The correct spelling is "Ground," referring to the solid surface of the earth or the basis for something.

- Growl: Correctly spelled. It is a low, guttural sound made by an animal or person when angry or threatening.

Grownd is the incorrectly spelled word.

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