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.
Citrin
The term Citrin when referring to Vitamin-P was the most active Bio-flavonoid in lemons, it was found to be Eriodictyol (but a more active form constituent was found there decades later).