- The definition of a subbasement is a floor below the basement.
An example of a subbasement is the level below the main basement of a building where the pipes and heater are located.
subbasement 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.
any floor or room below the principal basement
subbasement definition by American Heritage Dictionary
A floor beneath a main basement of a building.