The Online Etymology Dictionary is a free online dictionary that describes the origins of English-language words.
Douglas Harper (aka "The Sciolist") compiled the etymology dictionary to record the history and evolution of more than 30,000 words, including slang and technical terms. The core body of its etymology information stems from Weekley's "An Etymological Dictionary of Modern English". Other sources include the Middle English Dictionary and the Barnhart Dictionary of Etymology (by Robert Barnhart and others). In producing his large dictionary, Douglas Harper says that he is essentially and for the most part a compiler, an evaluator of etymology reports which others have made.
The Online Etymology Dictionary has been referenced by Ohio University's Library as a relevant etymological resource and cited in the Chicago Tribune as one of the "best resources for finding just the right word". It is cited in numerous articles as a source for explaining the history and evolution of words.
An etymological dictionary discusses the etymology of the words listed. Often, large dictionaries, such as the Oxford English Dictionary and Webster's, will contain some etymological information, without aspiring to focus on etymology.
Etymological dictionaries are the product of research in historical linguistics. For a large number of words in any language, the etymology will be uncertain, disputed, or simply unknown. In such cases, depending on the space available, an etymological dictionary will present various suggestions and perhaps make a judgement on their likelihood, and provide references to a full discussion in specialist literature.
The tradition of compiling "derivations" of words is pre-modern, found for example in Indian (nirukta), Arabic (al-ištiqāq) and also in Western tradition (in works such as the Etymologicum Magnum). Etymological dictionaries in the modern sense, however, appear only in the late 18th century (with 17th-century predecessors such as Vossius' 1662 Etymologicum linguae Latinae or Stephen Skinner's 1671 Etymologicon Linguae Anglicanae), with the understanding of sound laws and language change and their production was an important task of the "golden age of philology" in the 19th century.