ex·ter·nal·i·ty \ˌekˌstərˈnaləd.ē\noun (-es) 1. a.: the quality or state of being external or externalized; especially: objectivity < the externality of some writers > b.: externalism 1b 2.: something that is external (as an external object, event, or feature) < the externalities of wealth, of friends, of fame — Irwin Edman >