Wiktionary:Word of the day/Archive/2025/March

1. (geometry) A polyhedron with parallel ends of the same polygonal shape and size, the other faces being parallelogram-shaped sides.
   1. An object having the shape of a geometrical prism (sense 1).
   2. (construction) A cutting (“open passage at a level lower than the surrounding terrain, dug for a canal, railway, or road to go through”) or an embankment shaped like a prism (sense 1) or a number of prisms, such that its volume can be easily calculated.
   3. (crystallography) A crystal in which the faces are parallel to the vertical axis.
   4. (optics) A transparent block in the shape of a prism (sense 1), typically with triangular ends, used to reflect or refract light.
      1. (archaic) A spectrum produced by light being refracted through a prism.
2. (by extension, surveying) A retroreflector (“device which reflects light back to its source with minimal scattering”) which is usually attached to a surveying pole as a target for a total station which emits a light beam at the device and calculates how long it takes to be reflected back in order to measure distance.
3. (figurative) A perspective that colours one's perception.

The English rock band Pink Floyd’s album The Dark Side of the Moon, which features a prism on its cover, was released on this day in 1973.

1. (historical) Chiefly preceded by the: the dividing line between Western Europe and the Soviet controlled regions, especially during the Cold War (1947–1991).

The term was popularized by a speech given by Winston Churchill, the Prime Minister of the United Kingdom, at Westminster College in Fulton, Missouri, U.S.A., on this day in 1946.

1. (arithmetic) The arithmetic operator consisting of repeated exponentiation, by analogy with exponentiation being repeated multiplication and multiplication being repeated addition, ${\displaystyle ^{b}a}$ denoting ${\displaystyle a}$ to the power of ${\displaystyle a}$ to the power of ${\displaystyle \ldots }$ to the power of ${\displaystyle a}$, in which ${\displaystyle a}$ appears ${\displaystyle b}$ times.

The English mathematician Reuben Goodstein, who coined the term, died on this day 40 years ago in 1985.