symptom

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

• noun An indication of a disorder or disease, especially a subjective one such as pain, nausea, or weakness.
• noun A characteristic sign or indication of the existence of something else.

from The Century Dictionary.

• noun paralysis of the facial muscles for the automatic movements of expression, with retention of the power of voluntary motion.
• noun the occurrence of a paroxysm when the motor nerve of a limb is compressed in tetany.
• noun One of the departures from normal function or form which a disease presents, especially one of the more evident of such departures.
• noun Any sign or indication; that which indicates the existence of something else.

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

• noun (Med.) Any affection which accompanies disease; a perceptible change in the body or its functions, which indicates disease, or the kind or phases of disease.
• noun A sign or token; that which indicates the existence of something else.

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

• noun medicine A perceived change in some function, sensation or appearance of a person that indicates a disease or disorder, such as fever, headache or rash.
• noun Anything that indicates, or is characteristic of, the presence of something else, especially of something undesirable.

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

• noun (medicine) any sensation or change in bodily function that is experienced by a patient and is associated with a particular disease
• noun anything that accompanies X and is regarded as an indication of X's existence