Wave modelIn historical linguistics, the wave model or wave theory (German Wellentheorie) is a model of language change in which a new language feature (innovation) or a new combination of language features spreads from its region of origin, affecting a gradually expanding cluster of dialects. Dialect diffusion spreads from a given point of contact like waves on the water. The theory was intended as a substitute for the tree model, which did not seem to be able to explain the existence of some features, especially in the Germanic languages, by descent from a proto-language.
Areal featureIn geolinguistics, areal features are elements shared by languages or dialects in a geographic area, particularly when such features are not descended from a proto-language, or, common ancestor language. That is, an areal feature is contrasted to lingual-genealogically determined similarity within the same language family. Features may diffuse from one dominant language to neighbouring languages (see "sprachbund"). Genetic relationships are represented in the family tree model of language change, and areal relationships are represented in the wave model.
Comparative linguisticsComparative linguistics is a branch of historical linguistics that is concerned with comparing languages to establish their historical relatedness. Genetic relatedness implies a common origin or proto-language and comparative linguistics aims to construct language families, to reconstruct proto-languages and specify the changes that have resulted in the documented languages. To maintain a clear distinction between attested and reconstructed forms, comparative linguists prefix an asterisk to any form that is not found in surviving texts.
Kurgan hypothesisThe Kurgan hypothesis (also known as the Kurgan theory, Kurgan model, or steppe theory) is the most widely accepted proposal to identify the Proto-Indo-European homeland from which the Indo-European languages spread out throughout Europe and parts of Asia. It postulates that the people of a Kurgan culture in the Pontic steppe north of the Black Sea were the most likely speakers of the Proto-Indo-European language (PIE). The term is derived from the Turkic word kurgan (курга́н), meaning tumulus or burial mound.
Language familyA language family is a group of languages related through descent from a common ancestral language or parental language, called the proto-language of that family. The term "family" reflects the tree model of language origination in historical linguistics, which makes use of a metaphor comparing languages to people in a biological family tree, or in a subsequent modification, to species in a phylogenetic tree of evolutionary taxonomy. Linguists therefore describe the daughter languages within a language family as being genetically related.
