Definition - A geographical boundary that separates the linguistic features that demarcate dialects.

For example, some notable isoglosses are:
(1) the Benrath line, which distinguishes High German from the other West Germanic languages, and
(2) the La Spezia-Rimini Line, which distinguishes Northern Italian dialects from Central ones.

1. Major dialects are usually demarcated by multiple isoglosses.

Etymology -
The term derives from the Greek ísos, equal or similar, and glossa, tongue or language.

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