Axiom:Axiom of Unions/Also known as

Axiom of Unions: Also known as
The  is in fact most frequently found with the name Axiom of Union.

However, in some treatments of axiomatic set theory and class theory, for example Morse-Kelley set theory this name is used to mean something different.

Hence specifically uses the plural form ' for this, and reserves the singular form ' for that.

Other terms that can be found to refer to the :
 * the 
 * the 
 * the Union Axiom.