# Definition:Abscissa

## Definition

Consider the graph $y = \map f x$ of a real function $f$ embedded in a Cartesian plane.

The $x$ coordinate of a point $P = \tuple {x, y}$ on $f$ is known as the **abscissa** of $P$.

## Also see

## Historical Note

The term **abscissa** was used by Leonardo Fibonacci in his $1220$ work *Practica Geometriae*.

Some sources suggest that the word descends from translations of *Conics* by Apollonius.

Its use in the modern sense, as meaning the $x$ coordinate of a point in a Cartesian plane, may have been due to Stefano degli Angeli in his $1659$ work *Miscellaneum Hyperbolicum, et Parabolicum*.

The term entered the mathematical mainstream via the works of Gottfried Wilhelm von Leibniz, and some suggest that he may even have coined it.

## Linguistic Note

The term **abscissa** comes from the Latin term **linea abscissa**, which means **a line cut off**.

The same source gives the word **scissors**.

Some sources suggest that the word descends from translations of *Conics* by Apollonius, where the Greek word **ἀποτεμνομέναις** (**apotemnomenais**) appears.

The word is rarely used nowadays except in the context of the history of mathematics.

Its plural is correctly **abscissae** or (to be even more strictly classically correct) **abscissæ**.

However, the plural form of the term (when it is used at all) is commonly **abscissas**.

$\mathsf{Pr} \infty \mathsf{fWiki}$ has no strong opinion on what plural form is used, as it is considered obsolete and is not expected to appear often.

## Sources

- 1933: D.M.Y. Sommerville:
*Analytical Conics*(3rd ed.) ... (previous) ... (next): Chapter $\text I$. Coordinates: $2$. Coordinates - 1958: P.J. Hilton:
*Differential Calculus*... (previous) ... (next): Chapter $1$: Introduction to Coordinate Geometry (footnote) - 1972: Murray R. Spiegel and R.W. Boxer:
*Theory and Problems of Statistics*(SI ed.) ... (previous) ... (next): Chapter $1$: Rectangular co-ordinates - 1989: Ephraim J. Borowski and Jonathan M. Borwein:
*Dictionary of Mathematics*... (previous) ... (next): Entry:**abscissa** - 1998: David Nelson:
*The Penguin Dictionary of Mathematics*(2nd ed.) ... (previous) ... (next): Entry:**abscissa**(*plural***abscissae**) - 2008: David Nelson:
*The Penguin Dictionary of Mathematics*(4th ed.) ... (previous) ... (next): Entry:**abscissa**(*plural***abscissae**) - 2014: Christopher Clapham and James Nicholson:
*The Concise Oxford Dictionary of Mathematics*(5th ed.) ... (previous) ... (next): Entry:**abscissa**