On occasion, I have seen either first names or last names that have "saint" or its abbreviation "st." as part of their names.
Examples: Eugene Saint-Laurent
St. John Lestrange (from an HP fanfic written before the Lestranges' real names were given)
Can anyone tell me how/why this naming convention came about? I currently have a name for a character that uses this convention, and while she's from a fantasy/sci-fi world, I wanted to see if there was a real-world explanation for this.
EDIT: Holy cow, you guys are awesome. Thanks so much for your help!