1640s, "animating spirit," from Latin psyche, from Greek psykhe "the soul, mind, spirit; breath; life, one's life, the invisible animating principle or entity which occupies and directs the physical body; understanding" (personified as Psykhe, the beloved of Eros), akin to psykhein "to blow, cool," from PIE root *bhes- "to blow, to breathe" (source also of Sanskrit bhas-), "Probably imitative" [Watkins].
Also in ancient Greek, "departed soul, spirit, ghost," and often represented symbolically as a butterfly or moth. The word had extensive sense development in Platonic philosophy and Jewish-influenced theological writing of St. Paul (compare spirit (n.)). Meaning "human soul" is from 1650s. In English, psychological sense "mind," is attested by 1910.