Spira

Spira is a term of Latin origin meaning coil or spiral. In science, mathematics, architecture, and biology, it functions as a root or label for spiral forms and related concepts.

The most recognized historical usage is Spira mirabilis, the name given by Jacob Bernoulli to the logarithmic spiral, also called an equiangular spiral. This curve has the property that the angle between the tangent and the radial line is constant, making it self-similar under scaling. The logarithmic spiral appears in nature and art, including nautilus shells, weather patterns, and spiral galaxies, and it has applications in design, optics, and growth models.

In contemporary usage, spira often appears as a linguistic root in technical terms related to spirals, as well as in various proper names—such as surnames or brand names—depending on language and region. Because it is a general descriptor rather than a single noun, its precise meaning varies with context.

See also: spiral, Spira mirabilis, nautilus shell.