jäikus

Jäikus is a Finnish noun meaning rigidity or stiffness. It is formed from the adjective jäykkä ("stiff") with the abstract-noun suffix -us, and is found primarily in technical and academic contexts. Although jäykkyys is the more common everyday word for stiffness, jäikus appears in medical, biomechanical, and mathematical texts to denote a state of resisting deformation or movement.

In medical usage, jäikus describes muscular rigidity, such as the increased muscle tone that can occur in neurological disorders like Parkinson's disease, resulting in resistance to passive movement. In physics or engineering contexts, jäikus can refer to the rigidity of a material or structure, though in many cases jäykkyys or other terms like modulus are used depending on the precise concept.

Linguistically, jäikus is more formal and specialized than jäykkyys and may be encountered in dictionaries or scholarly writings. It is not commonly used in everyday speech, where jäykkyys is preferred.

See also: jäykkyys; jäykistyä; elastisuus.