The term Cantonese clearly derives its origin from "Canton", the old name given by Westerners to Guangzhou, the capital of Guangdong Province. Most likely, it is a metonymy corruption of the Cantonese pronunciation Gwong Dung, the name of the province, which used to be romanized as Kwang Tung. Interestingly, in Japanese, the name of the province is pronounced kanton, which seems to be the onyomi pronunciation of the kanji. This provides us with another clue about the history of this word.
This is a disambiguation page; that is, one that just points to other pages that might otherwise have the same name. If you followed a link here, you might want to go back and fix the link, so that it points to the appropriate page.