copula

noun

Etymology: Borrowed from Latin cōpula (“connection, linking of words”), from co- (“together”) + apere (“fasten”). Doublet of couple.

1. A word, usually a verb, used to link the subject of a sentence with a predicate (usually a subject complement or an adverbial), that unites or associates the subject with the predicate.

   “I begin by arguing in section 2 that there are in fact at least two Celtic copulas, a grammatical copula that simply spells out tense and agreement, and a substantive copula formed on a lexically listed verbal stem.”

   “The theory of conjunctively tensed copulae will be developed and stated with more precision in the following section.”

2. The bond or relationship by which two things are combined into a unity.

   “The fact that in milk the copula or bond is exceedingly slight is evident from the spontaneous resolution of milk when left in a vessel, its resolution, namely, into cream—a white substance of comparative consistency,—and a sourish fluid; also from its ready resolution when, merely by motion, it is turned into butter, or, by heat, into various kinds of curds.”

   “I quite correctly defined logical copulation by means [of] the copula of inclusion.”

3. A function that represents the association between two or more variables, independent of the individual marginal distributions of the variables.

   “In 2000, David X. Li, a banker with a doctorate in statistics who was then at RiskMetrics, part of J. P. Morgan Chase, began using mathematical functions called Gaussian copulas to estimate the likelihood of corporations’ dying in unison.”

   “There is little statistical theoretical theory for copulas. Sensitivity studies of estimation procedures and goodness-of-fit tests for copulas are unknown.”

4. A device that connects two or more keyboards of an organ.
5. The act of copulation; mating.