säteisiin

Säteisiin is the illative plural form of the Finnish noun säde, meaning ray or beam, especially a ray of light or other radiation. As an illative, säteisiin denotes movement or direction into multiple beams or into a field of rays. The corresponding singular illative form is säteeseen. In addition to the illative, the noun has common forms such as nominative säde (singular) and säteet (plural), as well as genitive säteen, partitive säteitä, inessive säteessä, and elative säteestä.

In usage, säde refers to a line or stream of light or radiation. The illative plural säteisiin appears in contexts describing entering, dispersing into, or being composed of multiple beams. For example, phrases like valon säteisiin or useisiin säteisiin jakautuminen convey entering or splitting into several rays, respectively. The construction is typical in scientific or descriptive prose when discussing optical phenomena, radiation patterns, or beam geometry.

Compared to other Finnish forms of säde, säteisiin is less common in everyday language and mainly appears in technical or explanatory writing. It is one of several inflected forms that enable precise expression of direction toward beams in plural.

Etymology and related forms are anchored in the base word säde, with standard Finnish inflection patterns applying. Related terms include säde (beam), säteet (rays, beams), and phrases describing light and radiation phenomena.