[ 'ʌɪsə(ʊ)glɒs ]
■ noun Linguistics a line on a map marking an area having a distinct linguistic feature.
Origin
early 20th cent.: from iso- + Gk glōssa 'tongue, word'.
ISOGLOSS
Meaning of ISOGLOSS in English
Concise Oxford English vocab. Сжатый оксфордский словарь английского языка. 2004