The Etymologies are one of the documents included in Volume V of The History of Middle-earth (The Lost Road). In his preface to that volume, Christopher Tolkien describes the Etymologies as "a kind of historical dictionary," and associates the work with the years 1937-1938, prior to Tolkien's work on The Lord of the Rings.
In the Etymologies, Tolkien provides a series of Elvish linguistic root syllables, or "bases". He then shows how each base evolved into various words in the various Elvish languages, primarily Quenya and Sindarin (then called "Noldorin"), but also about ten other variations. Although the derived words cannot necessarily be said to be in their final forms, as Tolkien's invented languages continued to evolve throughout his life, as Christopher Tolkien points out, this document "enormously increases the known vocabularies of the Elvish tongues".