The dit name (in French nom-dit [nɔ̃ di]) was a common French Canadian custom by which families often adopted an alternate surname. The practice lasted until the 19th century. The dit name poses challenges for genealogists confronted with different surnames in different documents, particularly if they are not familiar with the custom.
Dit and the feminine form dite translate as "called" and are the past participle of the French word dire "to say". A name such as Adolphe Guillet dit Tourangeau can translate as "Adolphe Guillet, called Tourangeau", where both "Gulliet" and "Tourangeau" are used as surnames, sometimes together and sometimes individually in different situations. The dit name carried the same legal weight as the original family name with regard to land transfers and the naming of children. Dit names were chosen for a variety of reasons, such as distinguishing one family from another nearby family with the same surname, or allowing an adopted child to retain both their birth and adopted family names.
A family's dit name often derived from a personal attribute, place of origin, or profession. It originated in the military, where those with the same name adopted noms de guerre to distinguish themselves. Children often adopted the dit name, sometimes dropping the original family name. Sometimes some of the children chose to take only the family name and others only the dit name.