Citron
A source of confusion is that "citron" or similar words in French (and other languages), and English are false friends, as they refer to the lemon. Indeed, into the 16th century, the English name "citron" included the lemon and perhaps the lime as well.
Watermelon
The citron melon or "makataan" - a variety with sweet yellow flesh that is cultivated around the world for fodder, and the production of citron peel and pectin.