Definitions for "Isogloss"
A line on a map between linguistically varied areas.
A line drawn on a map of a speech area to show the boundary of the presence of a particular form. These have been used in dialect studies to show where certain forms are and are not found. For example, a dialectal researcher might elicit data from speakers in several areas of the southern US to find the presence or absence of the word y'all in their dialect. He would use the data to draw an isogloss to divide where y'all was likely to be heard from where it would not likely be used. A group of such isoglosses could together form a dialectal boundary. Historical linguists like Georg Wenker to study the implementation of sound changes. Isolate A language that is unrelated to any other language and thus forms its own language family; for example, Basque.
A line on a dialect or language map that separates different dialects or languages. These lines are inherently dynamic and typically inaccurate.