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.
Citrus halimii
Citrus halimii or Mountain citron is a sour fruit variety belonging to the citrus papedas, not related to the true citron. It was first discovered and catalogued in 1973.