spectrum

Etymology

From Latin spectrum (“appearance, image, apparition”), from speciō (“look at, view”). Doublet of specter. See also scope.

noun

1. A range; a continuous, infinite, one-dimensional set, possibly bounded by extremes.
   As Mr. Obama prepared to take the oath, his approval rating touched a remarkable 70 percent in some polling — a reflection of good will across the political spectrum. November 7, 2012, Matt Bai, “Winning a Second Term, Obama Will Confront Familiar Headwinds”, in New York Times
2. Specifically, a range of colours representing light (electromagnetic radiation) of contiguous frequencies; hence electromagnetic spectrum, visible spectrum, ultraviolet spectrum, etc.
   Current 3G technologies can send roughly 1 bit of data - a one or a zero - per second over each 1 Hz of spectrum that the operator owns. October 30 2010, Jim Giles, “Jammed!”, in New Scientist
3. (psychology, education, usually with the) The autism spectrum.
4. (chemistry) The pattern of absorption or emission of radiation produced by a substance when subjected to energy (radiation, heat, electricity, etc.).
5. (mathematics, linear algebra) The set of eigenvalues of a matrix.
6. (mathematics, functional analysis) Of a bounded linear operator A, the set of scalar values λ such that the operator A—λI, where I denotes the identity operator, does not have a bounded inverse; intended as a generalisation of the linear algebra sense.
7. (abstract algebra, algebraic geometry) The set, denoted Spec(R), of all prime ideals of a given ring R, commonly augmented with a Zariski topology and considered as a topological space.
8. (obsolete) Specter, apparition.
9. The image of something seen that persists after the eyes are closed.