However, in Cornish, "goon" could be a mispronunciation of the word "gwenn" which means "white".
It's also possible you're thinking of the word "gwan" which means "weak" or "feeble".
It's important to note that the Cornish language is quite rare and not widely spoken, so it's possible there are variations in spelling and pronunciation.
If you can provide more context or information about where you encountered the word "goon", I might be able to offer a more accurate interpretation.