etymology (ĕtĭmŏlˈəjē) [key], branch of linguistics that investigates the history, development, and origin of words. It was this study that chiefly revealed the regular relations of sounds in the Indo-European languages (as described in Grimm's law) and led to the historical investigation of language in the 19th cent. In the 20th cent. linguists continued to use etymology to learn how meanings change, but they came to consider that the meaning of a form at a given time must be understood without reference to its history if it is to be understood at all. The term etymology has been replaced by the term derivation for the creation of combinations in a language, such as new nouns formed with the ending -ness. See grammar; dictionary.