Noun
eigenclass (plural eigenclasses)
(object-oriented programming) A hidden class associated with each specific instance of another class.
Singleton methods in Ruby live in a special, hidden class called the singleton class (it used to be referred to as the eigenclass, but singleton class is the current term).https://codequizzes.wordpress.com/2014/04/11/singleton-classes-in-ruby-aka-eigenclasses/