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]
"irrational fear, horror, or aversion; fear of an imaginary evil or undue fear of a real one," 1786, perhaps based on a similar use in French, abstracted from compounds in -phobia, the word-forming element from Greek phobos "fear, panic fear, terror, outward show of fear; object of fear or terror," originally "flight" (still the only sense in Homer), but it became the common word for "fear" via the notion of "panic flight" (compare phobein "put to flight; frighten"), from PIE root *bhegw- "to run" (source also of Lithuanian bėgu, bėgti "to flee;" Old Church Slavonic begu "flight," bezati "to flee, run;" Old Norse bekkr "a stream").
The psychological sense of "an abnormal or irrational fear" is attested by 1895. Hence also Phobos as the name of the inner satellite of Mars (discovered 1877) and named for Phobos, the personification of fear, in mythology a companion of Ares.