I was just reading the definition of "contiguous" in Black's. It wound up by saying "The term is not synonomous with "vicinal"." The word "vicinial" is not listed in Black's - seems a little strange, I guess "vicinal" is not a "legal" word...?.
vicinial - adj
1. of, pertaining to, or belonging to a neighborhood or district.
2. adjacent.
3. noting a crystal plane whose position varies very little from that of a fundamental plane of the form.
I certainly butchered the spelling in my original post - the word is "vicinal", not "vicinial".
Both vicinial and vicinal are similar in meaning "in the neighborhood, neighboring, adjacent" and that they have minor difference in actual use in describing something.
They are variations of Latin words where vicinial means joining and vicinal means in the neighborhood.