Merging A Saint

Is your ancestor’s last name “St. Clair”  or some other phrase starting with the word “Saint?” Is it possible that the “saint” was merged into the rest of the name resulting in Sinclair? Or is it possible your ancestor’s middle and last names “merged” into one? Sometimes when I tell people my name is “Michael Neill,” they think I am saying “Mike O’Neill.” Did something similar happen with your ancestor’s name?