Etymology focuses on finding the origins of words and how their meanings change throughout history; it's basically the analysis and study of the history of words.
Thus "Etymological dictionaries" will offer readers not just definitions, but rather explanations about each word, including what that word meant before and its meaning across time, even how it used to sound throughout time and places accordingly; hence the historical development of its meaning; looking at the roots of words and how they obtained their current meaning.
Some general dictionaries often contain etymological information, such as Webster's and Oxford, but dedicated"Etymological Dictionaries" are the output of research in linguistics.
Among some examples we find the "IEEDLatin" or (Etymological Dictionary of Latin & other Italic Languages) or the Indo-European Etymological Dictionary project of Leiden University also known as "IEDO" (its online version), or books like "The Etymologicon" and the "Barnhart Concise Dictionary of Etymology".
