degeneration

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

• noun The process of degenerating.
• noun The state of being degenerate.
• noun Medicine Gradual deterioration of specific tissues, cells, or organs with corresponding impairment or loss of function, caused by injury, disease, or aging.
• noun Biology The evolutionary decline or loss of a function, characteristic, or structure in an organism or species.
• noun Electronics Loss of or gain in power in an amplifier caused by unintentional negative feedback.

from The Century Dictionary.

• noun A progressive departure of a family from the normal condition: shown in the first generation by a nervous temperament, moral depravity, and excesses; in the second by tendency to apoplexy and severe neuroses frequently with alcoholism; in the third by mental derangement, suicide, and intellectual weakness; and in the fourth by hereditary imbecility, deformities, arrested development, and sterility.
• noun In geology, disintegration produced by weathering.
• noun Wallerian degeneration proceeding in a direction from the periphery toward the center.
• noun A loss or impairment of the qualities peculiar to the race or kind, or to a type; reduction to a lower type in some scale of being.
• noun Specifically Loss or impairment of natural or proper qualities; descent to an inferior state; the act of becoming or the state of having become inferior, especially with respect to moral qualities.
• noun In physiology, any process by which a tissue or substance becomes replaced by some other regarded as less highly organized, less complex in composition, of inferior physiological rank, or less suited for the performance of its original functions.
• noun A degenerate animal or plant; an organism of a degraded type.

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

• noun The act or state of growing worse, or the state of having become worse; decline; degradation; debasement; degeneracy; deterioration.
• noun (Physiol.) That condition of a tissue or an organ in which its vitality has become either diminished or perverted; a substitution of a lower for a higher form of structure.
• noun (Biol.) A gradual deterioration, from natural causes, of any class of animals or plants or any particular organ or organs; hereditary degradation of type.
• noun rare The thing degenerated.
• noun See under Amyloid, Caseous, etc.

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

• noun uncountable The process or state of growing worse, or the state of having become worse.
• noun uncountable That condition of a tissue or an organ in which its vitality has become either diminished or perverted; a substitution of a lower for a higher form of structure.
• noun uncountable Gradual deterioration, from natural causes, of any class of animals or plants or any particular organ or organs; hereditary degradation of type.
• noun countable A thing that has degenerated.

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

• noun the process of declining from a higher to a lower level of effective power or vitality or essential quality
• noun the state of being degenerate in mental or moral qualities
• noun passing from a more complex to a simpler biological form