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an abnormal lack of energy, esp as the result of a disease
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.



a morbid condition similar to sleep and characterized by immobility, absence of reactions to external stimuli, and marked weakening of all external signs of life (mors putativa).

Even the most extreme cases of lethargy can be distinguished from death, thereby precluding the possibility of erroneous burial of the living. Lethargy may be seen in hysteria, general exhaustion, and after intense agitation. An attack is sudden and lasts several hours to many days. Consciousness is usually retained: the patients perceive and remember what is happening around them but they do not react to it. The torpor associated with encephalitis and narcolepsy should be distinguished from lethargy.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.


A morbid condition of drowsiness or stupor; mental torpor.
A measure of the energy which has been lost by a neutron, equal to the natural logarithm of the ratio of the initial energy of a neutron to its energy at any given point in the slowing-down process.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.