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1570s, "affinity between certain things," from Middle French sympathie, from Late Latin sympathia "community of feeling, sympathy," from Greek sympatheia, from sympathes "having a fellow feeling, affected by like feelings," from syn- "together" (see syn-) + pathos "feeling" (see pathos).
In English, almost a magical notion at first; e.g. in reference to medicines that heal wounds when applied to a cloth stained with blood from the wound. Meaning "conformity of feelings" is from 1590s; sense of "fellow feeling" is first attested 1660s. An Old English loan-translation of sympathy was efensargung.
sympathy sym·pa·thy (sĭm'pə-thē)
A relation between parts or organs by which a disease or disorder in one induces an effect in the other.
Mental contagion, as in yawning induced by seeing another person yawn.
Mutual understanding or affection arising from a relationship or an affinity, in which whatever affects one correspondingly affects the other.