**The Collaborative International Dictionary of English v.0.48:**

Constant \Con"stant\, n.
1. That which is not subject to change; that which is
invariable.
[1913 Webster]
2. (Math.) A quantity that does not change its value; -- used
in countradistinction to variable.
[1913 Webster]
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.]