form class definition by Webster's New World
Webster's New World College Dictionary Copyright © 2010 by Wiley Publishing, Inc., Cleveland, Ohio. Used by arrangement with John Wiley & Sons, Inc.
Linguis. a class made up of words that occur in a distinctive position in constructions and have certain formal features in common, as the form class noun in English, made up of all words to which both the plural and possessive suffixes may be added
form class definition by American Heritage Dictionary
A set of words that have one or more grammatical or syntactic characteristics in common, such as the class of transitive verbs in English.