Hi Candy. "dit" means, basically "alias". If you go back to our first ancestor in America, Antoine, the most common spelling of his family name was "Terou". But he came to New France as a member of the french Army. And they had a custom to assign a name to each new recruit for identity purposes, as many if not most recruits were illiterate, and could not write their names. In Antoines' case he was assigned the name LaFerte, which some branches of out family still utilize. A smaller branch of my line uses the name Landrouche, and ii still don't know from where it came, but Gilbert Theroux, son of Theophile, and grandson of Andre the III started using the name and it stuck. there are other examples of different names common throughout the Theroux clan.
By the way, thank you for referring me to your chart within the Theroux Genforum page. However, that chart ends with your Michel, do you have any ancesters beyond him.