Isogloss

An isogloss, also called a heterogloss (see Etymology below), is the geographic boundary of a certain linguistic feature, such as the pronunciation of a vowel, the meaning of a word, or the use of some morphological or syntactic feature. Major dialects are typically demarcated by bundles of isoglosses, such as the Benrath line that distinguishes High German from the other West Germanic languages and the La Spezia–Rimini Line that divides the Northern Italian languages and Romance languages west of Italy from Central Italian dialects and Romance languages east of Italy. However, an individual isogloss may or may not have any coterminus with a language border. For example, the front-rounding of /y/ cuts across France and Germany, while the /y/ is absent from Italian and Spanish words that are cognates with the /y/-containing French words. One of the best-known isoglosses is the centum-satem isogloss. Similar to an isogloss, an isograph is a distinguishing feature of a writing system. Both concepts are also used in historical linguistics. Centum-satem isogloss The centum-satem isogloss of the Indo-European language family relates to the different evolution of the dorsal consonants of Proto-Indo-European (PIE). In the standard reconstruction, three series of dorsals are recognised: In some branches (for example Greek, Italic and Germanic), the palatals merged with the velars: PIE "tremble (inwardly)" became Latin cupiō "desire" and "hundred" became Latin centum (pronounced [kentum]); but "interrogative pronoun" became quō "how? where?". They are known as centum branches, named after the Latin word for hundred. In other branches (for example, Balto-Slavic and Indo-Iranian), the labiovelars merged with the velars: PIE became Vedic Sanskrit kopáyati "shaken" and became Avestan kō "who?"; but became Avestan satəm. They are known as satem branches, after the Avestan word for hundred. Since the Balto-Slavic family, the Indo-Iranian family, and the other satem families are spoken in adjacent geographic regions, they can be grouped by an isogloss: a geographic line separating satem branches on one side from centum branches on the other.