Meaning of isogloss

i•so•gloss

Pronunciation: (ī'su-glos", -glôs"), [key]
— n.
  1. (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.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.