Definition of "isogloss"

Bloch thinks (and we agree with him) that details of isogloss will probably not bear out this kind of grouping.

1921, The Calcutta Review, Calcutta: University of Calcutta, page 285

There was also a tendency to treat transitive verbs passively, as in Hurrian and Urarṭian; it must, however, be emphasized that this phenomenon may also be considered as an isogloss rather than as an indication of genetic relationship.

1970, W[illiam] F[oxwell] Albright, T[homas] O[den] Lambdin, “The Evidence of Language”, in I[orwerth] E[iddon] S[tephen] Edwards, C[yril] J[ohn] Gadd, N[icholas] G[eoffrey] L[emprière] Hammond, editors, The Cambridge Ancient History, 3rd edition, volumes I, part 1 (Prolegomena and Prehistory), Cambridge: Cambridge University Press, published 2000, section IV (Sumerian, Hurrian, Urarṭian, Elamite), page 154

The convergence of multiple isoglosses on a map, a "bundle", indicates a boundary between one regional dialect and another.

2005, Brian D. Joseph, Carol G. Preston, Dennis R. Preston, editors, Language Diversity in Michigan and Ohio: Towards Two State Linguistic Profiles, Ann Arbor, Mich.: Caravan Books, page 29