kehän

Kehän is the genitive singular form of the Finnish noun kehä, which means ring, circle or circular band. As a grammatical form, kehän is used to indicate possession or a relationship to the ring or circular object, for example kehän pituus (the circumference of the circle) or a description such as kehässä oleva väri (the color of the ring). The same form also appears in compound expressions where the ring or circular feature is the reference point.

In geometry and mathematics, kehän pituus refers to the circumference, the distance around a circle. The circumference is commonly expressed by formulas such as C = 2πr or C = πd, where r is the radius and d is the diameter. The term ympärysmitta is another Finnish word used for circumference, and kehän pituus may be used interchangeably in many contexts.

In Finnish urban planning and transportation terminology, kehä commonly denotes a beltway or ring road around a city. The Helsinki area famously uses Kehä I, Kehä II and Kehä III to describe three concentric ring roads that connect suburbs and relieve city-center traffic. The concept of a kehä can be applied to other metropolitan areas as well, referring to similar ring-shaped road systems or corridors.

Grammatical note: Kehä is a regular Finnish noun, and kehän is its genitive singular form. This form appears in phrases describing the circle or ring, its properties, or its relation to other objects.