constant

from The American Heritage® Dictionary of the English Language, 5th Edition.

• adjective Continually occurring; persistent: synonym: continual.
• adjective Regularly recurring.
• adjective Unchanging in nature, value, or extent; invariable.
• adjective Steadfast in purpose, loyalty, or affection; faithful. synonym: faithful.
• noun Something that is unchanging or invariable.
• noun A quantity assumed to have a fixed value in a specified mathematical context.
• noun An experimental or theoretical condition, factor, or quantity that does not vary or that is regarded as invariant in specified circumstances.

from The Century Dictionary.

• Fixed; not varying; unchanging; permanent; immutable; invariable.
• Specifically In natural history, not subject to variation; not varying in number, form, color, appearance, etc., in the species or group; always present: as, the middle stria is constant, though the lateral ones are often absent; the reniform spot is constant, but the other markings are subject to variation.
• Continuing for a long or considerable length of time; continual; enduring; lasting in or retaining a state, quality, or attribute; incessant; ceaseless: as, constant change.
• Regularly recurring; continually renewed or reiterated; continual: persistent: as, the constant ticking of a clock; the constant repetition of a word; constant moans or complaints.
• Fixed or firm in mind, purpose, or principle; not easily swayed; unshaken; steady; stable; firm or unchanging, as in affection or duty; faithful; true; loyal; trusty.
• Fixed in belief or determination; insistent; positive.
• Fixed; stable; solid: opposed to fluid.
• Strong; steady.
• Consistent; logical; reasonable.
• Indisputably true; evident.
• Synonyms and Steadfast, stable, unchanging, unalterable, invariable, perpetual, continual; resolute, firm, stanch, unshaken, unwavering, determined; persevering, assiduous, unremitting; trusty.
• noun That which is not subject to change; something that is always the same in state or operation, or that continually occurs or recurs.
• noun Specifically— In mathematics, a quantity which is assumed to be invariable throughout a given discussion; in the differential calculus, a quantity whose value remains fixed while others vary continuously. Although the constants do not vary by the variation of those quantities that are at first considered as variables, some or all of them may be conceived to vary in a second kind of change, called the variation of constants. A quantity which upon one supposition would remain constant becomes variable by the introduction of another supposition. Thus, taking into account the earth's attraction only, the longitude of the moon's node is constant, but by the attraction of the sun and planets its place is slowly changed. In this case one of the constants is said to vary. In algebra the unknown quantities are considered as variables, the known quantities and coefficients as constants.
• noun In physics, a numerical quantity, fixed under uniform conditions, expressing the value of one of the physical properties of a certain substance. Thus, the physical constants of ice are the values of its specific gravity, melting-point, coefficient of expansion, index of refraction, electrical conductivity, etc. Similarly, in the case of a physical instrument a constant is a fixed value depending upon its dimensions, etc. Thus, the constant of a tangent galvanometer is the radius of its coil divided by the number of coils into 6.28318+.

from the GNU version of the Collaborative International Dictionary of English.

• adjective obsolete Firm; solid; fixed; immovable; -- opposed to fluid.
• adjective Not liable, or given, to change; permanent; regular; continuous; continually recurring; steadfast; faithful; not fickle. Opposite of changeable and variable.
• adjective (Math. & Physics) Remaining unchanged or invariable, as a quantity, force, law, etc.
• adjective obsolete Consistent; logical.
• noun That which is not subject to change; that which is invariable.
• noun (Math.) A quantity that does not change its value; -- used in countradistinction to variable.
• noun (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.
• noun (Physics) A number expressing some property or condition of a substance or of an instrument of precision.
• noun (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.
• noun (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″.47.
• noun (Math.) one whose value is absolutely the same under all circumstances, as the number 10, or any numeral.
• noun an undetermined constant in a differential equation having the same value during all changes in the values of the variables.
• noun (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.
• noun (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.
• noun (Math.) an undetermined constant added to every result of integration.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• adjective Unchanged through time or space; permanent.
• adjective Consistently recurring over time; persistent
• adjective Steady in purpose, action, feeling, etc.
• noun That which is permanent or invariable.
• noun algebra A quantity that remains at a fixed value throughout a given discussion.
• noun sciences Any property of an experiment, determined numerically, that does not change under given circumstances.
• noun computing An identifier that is bound to an invariant value.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• adjective uninterrupted in time and indefinitely long continuing
• noun a number representing a quantity assumed to have a fixed value in a specified mathematical context
• adjective steadfast in purpose or devotion or affection
• noun a quantity that does not vary
• adjective unvarying in nature