A vicinal is a logological term for a word where all its letters have "alphabetic neighbors". For instance, if a word has an "O" in it, to be a vicinal it must also have an "N" and/or a "P". If none of the letters have alphabetic neighbors, it is known as a nonvicinal.
Some common vicinals: Blacksmith, Documents, Done, Fights, High, On, Sport, This
Some common nonvicinals: As, In, Intelligibility, Lacqueying, Mississippi, Mortgage, The
Some common words that are neither vicinals nor nonvicinals (i.e. some, not all, letters have alphabetic neighbors): About, Almanac, Dictionary, Times, Wisconsin