[ahy-suh-glos, -glaws] 
| (in the study of the geographical distribution of dialects) a line on a map marking the limits of an area within which a feature of speech occurs, as the use of a particular word or pronunciation. |
| i·so·gloss (ī'sə-glôs', -glŏs') n. A geographic boundary line delimiting the area in which a given linguistic feature occurs. [iso- + Greek glōssa, language, tongue.] i'so·gloss'al adj. |
səˌglɒs