In linguistics, a catena (English pronunciation: , plural catenas or catenae; from Latin for "chain") is a unit of syntax and morphology, closely associated with dependency grammars. It is a more flexible and inclusive unit than the constituent and may therefore be better suited than the constituent to serve as the fundamental unit of syntactic and morphosyntactic analysis. The catena has served as the basis for the analysis of a number of phenomena of syntax, such as idiosyncratic meaning, ellipsis mechanisms (e.g. gapping, stripping, VP-ellipsis, pseudogapping, sluicing, answer ellipsis, comparative deletion), predicate-argument structures, and discontinuities (topicalization, wh-fronting, scrambling, extraposition, etc.). The catena concept has also been taken as the basis for a theory of morphosyntax, i.e. for the extension of dependencies into words; dependencies are acknowledged between the morphs that constitute words. While the catena concept has been applied mainly to the syntax of English, other works are also demonstrating its applicability to the syntax and morphology of other languages. Descriptions and definitions Two descriptions and two definitions of the catena unit are now given. Catena (everyday description) Any single word or any combination of words that are linked together by dependencies. Catena (graph-theoretic description) In terms of graph theory, any syntactic tree or connected subgraph of a tree is a catena. Any individual element (word or morph) or combination of elements linked together in the vertical dimension is a catena. Sentence structure is conceived of as existing in two dimensions. Combinations organized along the horizontal dimension (in terms of precedence) are called strings, whereas combinations organized along the vertical dimension (in terms of dominance) are catenae. In terms of a cartesian coordinate system, strings exist along the x-axis, and catenae along the y-axis. Catena (informal graph-theoretic definition) Any single word or any combination of words that are continuous in the vertical dimension, that is, with respect to dominance (y-axis). Catena (formal graph-theoretic definition) Given a dependency tree T, a catena is a set S of nodes in T such that there is one and only one member of S that is not immediately dominated by any other member of S. Four units An understanding of the catena is established by distinguishing between the catena and other, similarly defined units. There are four units (including the catena) that are pertinent in this regard: string, catena, component, and constituent. The informal definition of the catena is repeated for easy comparison with