A "Dit Name" in French surnames, could be considered a second surname used to differentiate between families of the same surname. My 7th g-Grandfather Pierre Lebeau, was born in Paris France about 1700. He immigrated to New France in the early 1700's and took the name "Pierre Lebeau dit Lajeunesse". His children were born under the surname "Lebeau dit Beaufils".
My 6th g-Grandfather, Pierre Etienne Lebeau dit Beaufils, named the 6 children from his first wife "Lebeau dit Caza" the "Caza" probally coming from the childrens maternal grandmother "Cazabaun" He named the 8 children from his second wife "Lebeau dit Beaufils"
I decend from the "Lebeau dit Caza" line. Parrish records in the 1800's might list an individual under the "Lebeau" surname in one entry and under the "Caza" name in another entry for the same person.
Sure makes it intresting in researching a family when the surname changes often