Etymology (i/) is the study of the history of words, their origins, and how their form and meaning have changed over time. By extension, the term "the etymology (of a word)" means the origin of the particular word and for place names, there is a specific term, toponymy.
For Greek—with a long written history—etymologists make use of texts, and texts about the language, to gather knowledge about how words were used during earlier periods and when they entered the language. Etymologists also apply the methods of comparative linguistics to reconstruct information about languages that are too old for any direct information to be available.
By analyzing related languages with a technique known as the comparative method, linguists can make inferences about their shared parent language and its vocabulary. In this way, word roots have been found that can be traced all the way back to the origin of, for instance, the Indo-Europeanlanguage family.
The word etymology derives from the Greek word ἐτυμολογία (etumología), itself from ἔτυμον (étumon), meaning "true sense", and the suffix -logia, denoting "the study of".
In linguistics, the term etymon refers to a word or morpheme (e.g., stem or root) from which a later word derives. For example, the Latin word candidus, which means "white", is the etymon of English candid.
Diagram showing relationships between etymologically-related words
Etymologists apply a number of methods to study the origins of words, some of which are:
Philological research. Changes in the form and meaning of the word can be traced with the aid of older texts, if such are available.
Making use of dialectological data. The form or meaning of the word might show variations between dialects, which may yield clues about its earlier history.
The comparative method. By a systematic comparison of related languages, etymologists may often be able to detect which words derive from their common ancestor language and which were instead later borrowed from another language.
The study of semantic change. Etymologists must often make hypotheses about changes in the meaning of particular words. Such hypotheses are tested against the general knowledge of semantic shifts. For example, the assumption of a particular change of meaning may be substantiated by showing that the same type of change has occurred in other languages as well.