equilibrium

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

• noun A condition in which all acting influences are canceled by others, resulting in a stable, balanced, or unchanging system.
• noun Mental or emotional balance.
• noun Physics The state of a body or physical system at rest or in unaccelerated motion in which the resultant of all forces acting on it is zero and the sum of all torques about any axis is zero.
• noun The state of a chemical reaction in which its forward and reverse reactions occur at equal rates so that the concentration of the reactants and products does not change with time.
• noun The state of a system in which more than one phase exists and exchange between phases occurs at equal rates so that there is no net change in the composition of the system.

from The Century Dictionary.

• noun Equipoise; the state of being equally balanced; a situation of a body in which the forces acting on it balance one another; also, a determination of forces such that they balance one another, so that their resultant vanishes.
• noun The state of balance of any causes, powers, or motives, so that no effect is produced.
• noun A state of just poise; a position of due balance.
• noun In the fine arts: The just poise or balance of a figure or other object, making it appear to stand firmly. The properly balanced disposition or arrangement of objects, lights, shadows, etc.
• noun Equality of influence or effect; due or just relationship.
• noun Indifferent or neutral equilibrium, when the vertical gradient of temperature in still air is exactly equal to the adiabatic rate in moving air, and a disturbed mass stays in its new location.
• noun Unstable equilibrium, when the vertical gradient of temperature in still air is greater than the adiabatic rate in moving air. In this ease the mass of air when once started in vertical motion continues to rise or fall as the case may be, because the thermodynamic change in its own temperature is less than the change actually existing in the surrounding atmosphere. A thunder-storm, with its ascending currents and formation of tall cumuli, illustrates unstable equilibrium.
• noun In chem.: An assumed condition of a mass consisting of the same or of different kinds of matter, in which apparently no chemical change is going on, but in which it is imagined that individual atoms are exchanging places with others of exactly similar character, so that in a given (perhaps extremely short) time many molecules may be decomposed and precisely as many molecules, of absolutely similar character, formed.
• noun The equilibrium of a liquid cooled, out of contact with its solid phase, below the temperature of equilibrium between the liquid and the solid; or of a liquid heated, out of contact with its vapor, above the temperature of equilibrium between the liquid and the vapor having a pressure equal to the actual pressure on the liquid. Water, free from ice, may be cooled many degrees below its usual freezing-point; when brought into contact with a fragment of ice, sometimes when disturbed mechanically, part of the water instantly freezes, and the temperature rises, from that of the labile equilibrium of water alone, to that of the stable equilibrium between water and ice.

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

• noun Equality of weight or force; an equipoise or a state of rest produced by the mutual counteraction of two or more forces.
• noun A level position; a just poise or balance in respect to an object, so that it remains firm; equipoise.
• noun A balancing of the mind between motives or reasons, with consequent indecision and doubt.
• noun (Steam Engine) a balanced valve. See under Valve.

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

• noun The condition of a system in which competing influences are balanced, resulting in no net change.
• noun physics The state of a body at rest or in uniform motion in which the resultant of all forces on it is zero.
• noun chemistry The state of a reaction in which the rates of the forward and reverse reactions are the same.
• noun Mental balance.

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

• noun a stable situation in which forces cancel one another
• noun equality of distribution
• noun a sensory system located in structures of the inner ear that registers the orientation of the head
• noun a chemical reaction and its reverse proceed at equal rates