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The Collaborative International Dictionary of English v.0.48 (gcide)

Constant \Con"stant\ (k[o^]n"stant), a. [L. onstans, -antis, p.
pr. of constare to stand firm, to be consistent; con- stare
to stand: cf. F. constant. See {Stand} and cf. {Cost}, v. t.]
1. Firm; solid; fixed; immovable; -- opposed to {fluid}.
[Obs.]
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If . . . you mix them, you may turn these two fluid
liquors into a constant body. --Boyle.
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2. Not liable, or given, to change; permanent; regular;
continuous; continually recurring; steadfast; faithful;
not fickle. Opposite of {changeable} and {variable}.
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Both loving one fair maid, they yet remained
constant friends. --Sir P.
Sidney.
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I am constant to my purposes. --Shak.
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His gifts, his constant courtship, nothing gained.
--Dryden.
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Onward the constant current sweeps. --Longfellow.
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3. (Math. & Physics) Remaining unchanged or invariable, as a
quantity, force, law, etc.
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4. Consistent; logical. [Obs.] --Shak.

Syn: Fixed; steadfast; unchanging; permanent; unalterable;
immutable; invariable; perpetual; continual; resolute;
firm; unshaken; determined.

Usage: {Constant}, {Continual}, {Perpetual}. These words are
sometimes used in an absolute and sometimes in a
qualified sense. Constant denotes, in its absolute
sense, unchangeably fixed; as, a constant mind or
purpose. In its qualified sense, it marks something as
a "standing" fact or occurence; as, liable to constant
interruptions; constantly called for. Continual, in
its absolute sense, coincides with continuous. See
{Continuous}. In its qualified sense, it describes a
thing as occuring in steady and rapid succession; as,
a round of continual calls; continually changing.
Perpetual denotes, in its absolute sense, what
literally never ceases or comes to an end; as,
perpetual motion. In its qualified sense, it is used
hyperbolically, and denotes that which rarely ceases;
as, perpetual disturbance; perpetual noise; perpetual
intermeddling.
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Constant \Con"stant\, n.
1. That which is not subject to change; that which is
invariable.
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2. (Math.) A quantity that does not change its value; -- used
in countradistinction to {variable}.
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3. (Astron.) A number whose value, when ascertained (as by
observation) and substituted in a general mathematical
formula expressing an astronomical law, completely
determines that law and enables predictions to be made of
its effect in particular cases.
[Webster 1913 Suppl.]

4. (Physics) A number expressing some property or condition
of a substance or of an instrument of precision; as, the
dielectric constant of quartz; the collimation constant of
a transit instrument.
[Webster 1913 Suppl.]

5. (Computers) a data structure that does not change during
the course of execution of a program. It may be a number,
a string, or a more complex data structure; -- contrasted
with {variable}.
[PJC]

{Aberration constant}, or {Constant of aberration} (Astron.),
a number which by substitution in the general formula for
aberration enables a prediction to be made of the effect
of aberration on a star anywhere situated. Its value is
20[sec].47.

{Absolute constant} (Math.), one whose value is absolutely
the same under all circumstances, as the number 10, or any
numeral.

{Arbitrary constant}, an undetermined constant in a
differential equation having the same value during all
changes in the values of the variables.

{Gravitation constant} (Physics), the acceleration per unit
of time produced by the attraction of a unit of mass at
unit distance. When this is known the acceleration
produced at any distance can be calculated.

{Solar constant} (Astron.), the quantity of heat received by
the earth from the sun in a unit of time. It is, on the C.
G. S. system, 0.0417 small calories per square centimeter
per second. --Young. [Webster 1913 Suppl.]

{Constant of integration} (Math.), an undetermined constant
added to every result of integration.
[1913 Webster Webster 1913 Suppl.]