conservation

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

• noun The act or process of conserving.
• noun Preservation or restoration from loss, damage, or neglect.
• noun The protection, preservation, management, or restoration of wildlife and of natural resources such as forests, soil, and water.
• noun The maintenance of a physical quantity, such as energy or mass, during a physical or chemical change.

from The Century Dictionary.

• noun The act of conserving,guarding, or keeping with care; preservation from loss, decay, injury, or violation; the keeping of a thing in a safe or entire state.
• noun Persistence; perdurance; permanence.
• noun In England, a court or board of commissioners having jurisdiction over a port (as London, Liverpool, etc.) or of a river (as the Thames, the Mersey, etc.), and charged with the regulation as well as the conservation of its navigation, fisheries, etc.

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

• noun The act of preserving, guarding, or protecting; the keeping (of a thing) in a safe or entire state; preservation.
• noun (Astron.) the principle that the radius vector drawn from a planet to the sun sweeps over equal areas in equal times.
• noun (Mech.) the principle that the total energy of any material system is a quantity which can neither be increased nor diminished by any action between the parts of the system, though it may be transformed into any of the forms of which energy is susceptible.

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

• noun The act of preserving, guarding, or protecting; the keeping (of a thing) in a safe or entire state; preservation.
• noun A wise use of natural resources.

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

• noun (physics) the maintenance of a certain quantities unchanged during chemical reactions or physical transformations
• noun an occurrence of improvement by virtue of preventing loss or injury or other change
• noun the preservation and careful management of the environment and of natural resources