Variorum: An edition of an author's work that includes multiple commentaries. It can also refer to a work that brings together all known editions of a text--for example, this variorum edition of Chaucer's writings.
Variorum (vahr-ee-OR-um) is the plural of the Latin varius; its first written citation in an English text, in 1728, was in the phrase "editio cum notis variorum" ("an edition with various notes"). In Latin, the word is a possessive (or genitive); in English today, it's used as a noun.
Hat tip to John McIntyre at You Don't Say for introducing me to this word. (See last paragraph of his post.)