1885, in the criminal psychology sense, a back-formation from psychopathic.

The Daily Telegraph had, the other day, a long article commenting on a Russian woman who had murdered a little girl. A Dr. Balinsky prevailed upon the jury to give a verdict of acquittal, because she was a "psychopath." The Daily Telegraph regards this term as a new coinage, but it has been long known amongst Spiritualists, yet in another sense. [The Medium and Daybreak, Jan. 16, 1885]

The case alluded to, and the means of acquittal, were briefly notorious in England and brought the word into currency in the modern sense.

1847, from psychopathy on model of German psychopatisch, from Greek psykhē "mind" (see psyche) + pathos "suffering" (from PIE root *kwent(h)- "to suffer").

1835, from Greek psykhopompos "spirit-guide," a term applied to Charon, Hermes Trismegistos, Apollo; from psykhē "the soul, mind, spirit" (see psyche) + pompos "guide, conductor."

1847, "mental derangement," Modern Latin, from Greek psykhē "mind" (see psyche) + -osis "abnormal condition." Greek psykhosis meant "a giving of life; animation; principle of life."