Koostub

Koostub is an Estonian verb form meaning is formed from or consists of. It is the present tense, third‑person singular form of the verb koostuma, used to describe the composition or arrangement of a thing, group, or system. In everyday language, the more common synonym is koosneb, but koostub appears in formal or technical contexts where emphasis is placed on the act of forming from components.

Usage of koostub typically involves a subject that is described as being made up of other parts. For example: "Süsteem koostub kolmest moodulist," meaning "The system consists of three modules." Another example: "Meeskond koostub viiest liikmest," meaning "The team is made up of five members." In many contexts, editors and writers may alternate with related forms such as koosneb or koostuv depending on tone and register.

Etymology and morphology are grounded in the Estonian concept of composition and assembly. The form koostub conveys a dynamic sense of building or being formed from parts, which can be useful in technical, scientific, or descriptive prose.

See also: Estonian language, Estonian grammar, word formation, and related verbs describing composition or assembly.