英语词源字典 - 在线词源网站

ago (adj.)[ago 词源字典]: early 14c., shortened form of Old English agan, agone "departed, passed away," past participle of an obsolete verb ago "to go forth," formed from a- "away" (perhaps here used as an intensive prefix) + gan "go" (see go (v.)). Agone remains a dialectal variant.[ago etymology, ago origin, 英语词源]
depart (v.): mid-13c., "part from each other," from Old French departir (10c.) "to divide, distribute; separate (oneself), depart; die," from Late Latin departire "divide" (transitive), from de- "from" (see de-) + partire "to part, divide," from pars (genitive partis) "a part" (see part (n.)).

As a euphemism for "to die" (to depart this life; compare Old French departir de cest siecle) it is attested from c. 1500, as is the departed for "the dead," singly or collectively. Transitive lingers in some English usages; the wedding service was till death us depart until 1662. Related: Departed; departing.
Manes (pl.): "Gods of the Lower World," in Roman religion, from Latin manes "departed spirit, ghost, shade of the dead, deified spirits of the underworld," usually said to be from Latin manus "good," thus properly "the good gods," a euphemistic word, but Tucker suggests a possible connection instead to macer, thus "the thin or unsubstantial ones."
psyche (n.): 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.
underworld (n.): c. 1600, "the lower world, Hades, place of departed souls," also "the earth, the world below the skies," as distinguished from heaven. Similar formation in German unterwelt, Dutch onderwereld, Danish underverden. Meaning "lower level of society" is first recorded 1890; "criminals and organized crime collectively" is attested from 1900.