alethonym
The true name of a person.
rare
“Samuel Langhorne Clemens” is the alethonym of “Mark Twain”.
Where it comes from
From Ancient Greek ἀληθής (alēthḗs, “true”) and ὄνυμα (ónuma, “name”), equivalent to aletho- + -onym.
Adapted from the Wiktionary entry alethonym (CC BY-SA 4.0).