A vicinal is a logological

Logology

Logology is the study of recreational linguistics, an activity that encompasses a wide variety of word games and wordplay emphasizing letter patterns...

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 vicinals:

• Blacksmith
• Documents
• Done
• Fights
• High
• On
• Sport
• This

Some nonvicinals:

• As
• In
• Intelligibility
• Lacqueying
• Mississippi
• Mortgage
• The

Some words that are neither:

• About
• Almanac
• Dictionary
• Times
• Wisconsin