Noah Webster's New International Dictionary of the English Language

1. (n.) Feeling corresponding to that which another feels; the quality of being affected by the affection of another, with feelings correspondent in kind, if not in degree; fellow-feeling.

2. (n.) An agreement of affections or inclinations, or a conformity of natural temperament, which causes persons to be pleased, or in accord, with one another; as, there is perfect sympathy between them.

3. (n.) Kindness of feeling toward one who suffers; pity; commiseration; compassion.

4. (n.) The reciprocal influence exercised by the various organs or parts of the body on one another, as manifested in the transmission of a disease by unknown means from one organ to another quite remote, or in the influence exerted by a diseased condition of one part on another part or organ, as in the vomiting produced by a tumor of the brain.

5. (n.) That relation which exists between different persons by which one of them produces in the others a state or condition like that of himself. This is shown in the tendency to yawn which a person often feels on seeing another yawn, or the strong inclination to become hysteric experienced by many women on seeing another person suffering with hysteria.

6. (n.) A tendency of inanimate things to unite, or to act on each other; as, the sympathy between the loadstone and iron.

7. (n.) Similarity of function, use office, or the like.