c. 1600, "natural aversion, hostile feeling toward," from Latin antipathia, from Greek antipatheia, abstract noun from antipathes "opposed in feeling, having opposite feeling; in return for suffering;" also "felt mutually," from anti "opposite, against" (see anti-) + pathein "to suffer, feel" (from PIE root *kwent(h)- "to suffer").

An abuse has crept in upon the employment of the word Antipathy. ... Strictly it does not mean hate,—not the feelings of one man set against the person of another,—but that, in two natures, there is an opposition of feeling. With respect to the same object they feel oppositely. [Janus, or The Edinburgh Literary Almanack, 1826]

Proto-Indo-European root meaning "to suffer."

It forms all or part of: anthropopathy; antipathy; apathy; empathy; idiopathy; nepenthe; osteopathy; -path; pathetic; -pathic; patho-; pathogenic; pathognomonic; pathology; pathos; -pathy; psychopathic; sympathy.

It is the hypothetical source of/evidence for its existence is provided by: Greek pathos "suffering, feeling, emotion, calamity," penthos "grief, sorrow;" Old Irish cessaim "I suffer;" Lithuanian kenčiu, kentėti "to suffer," pakanta "patience."