The term

The terms **UMBRAL CALCULUS** and **UMBRAL NOTATION** were coined
by James Joseph Sylvester (1814-1897).

**UNDECAGON.** The earlier term for an 11-sided polygon, *hendecagon*
(or *endecagon*), is found in English in 1704 in *Lexicon technicum,
or an universal English dictionary of arts and sciences,* by John Harris
(OED2).

*Undecagon* is found in English in 1728 in Chambers' *Cyclopedia.*

**UNDECIDABLE** was used by Kurt G鐰el (1906-1978) in 1931 in the
title *Uber formal unentscheidbare S酹ze der Principia Mathematica und
verwandter Systeme* (On Formally Undecidable Propositions in Principia
Mathematica and Related Systems).

**UNIFORM DISTRIBUTION.** Uspensky (1937) page 237 reads "A stochastic
variable is said to have uniform distribution of probability if probabilities
attached to two equal intervals are equal." This is a slight variant of
the modern terminology, which would be "a variable is said to be uniformly
distributed" or "a variable from the uniform distribution" [James A. Landau].

The phrase **UNIFORMLY MOST POWERFUL** occurs in R. A. Fisher, "Two
New Properties of Mathematical Likelihood," *Proceedings of the Royal
Society,* Series A, vol. 144 (1934) [James A. Landau].

The term **UNIVERSAL ALGEBRA** was first used by James Joseph Sylvester
(1814-1897) in a paper, "Lectures on the Principles of Universal Algebra,"
published in the *American Journal of Mathematics,* vol. 6, 1884,
according to Whitehead [*Encyclopaedia Britannica,* article: Algebraic
Structures].

**UNKNOWN.** In *Miscellanea Berolinensia* (1710) Leibniz used
the phrase "incognita, *x,*" which is translated "the unknown *x.*"

*Unknown* is found in English in 1817 in the sentence "The demonstration
is by resolution of a quadratic equation involving several unknown" in
*Algebra
of the Hindoos, with arithmetic and mensuration* by Henry T. Colebrooke
(OED2).