isogloss
noun
iso·gloss ˈī-sə-ˌgläs 
-ˌglȯs
1
: a boundary line between places or regions that differ in a particular linguistic feature
2
: a line on a map representing an isogloss
isoglossal
ˌī-sə-ˈglä-səl
adjective -ˈglȯ-
isoglossic
ˌī-sə-ˈglä-sik
adjective -ˈglȯ-
Word History
Etymology
International Scientific Vocabulary is- + Greek glōssa language — more at gloss
First Known Use
1925, in the meaning defined at sense 1