By-name, a term commonly used in relation to a person's nickname or second name, can have several antonyms. One antonym could be a formal name, a name given to a person at birth or on official documents. Another could be a surname, which is a family name indicating lineage. A third antonym could be a title, such as Mr., Mrs., or Dr., which denotes a person's rank or profession. Finally, a fourth antonym could be anonymity, indicating the state of being unknown or unrecognized. These antonyms contrast with the informality and familiarity implied by a by-name.