Atropos - Ἄτροπος, meaning not turning, inflexible, unchangeable; one of the three Fates
Charon - Χᾰ́ρων, derived from the Ancient Greek χαροπός, referring to bright, cheerful eyes; the ferryman to the underworld
Erebus - Ἔρεβος possibly from the Proto-Indo-European *h₁régʷos, meaning darkness, twilight; the nothingness before the universe existed
Hades - ᾍδης, possibly from the Proto-Indo-European *n̥weyd-, meaning that which is not seen. ironically, he is also known as Aidoenus, which evolved without the negative prefix from the Greek verb εἴδομαιto (eídomai), which is be seen, to appear; the king of the underworld
Hecate - Ἑκᾰ́τη, unclear origins, possibly the Ancient Greek for will, as in, she who does that which is her will; goddess of the night, witchcraft and necromancy, among others
Hermes - Ἑρμῆς , unclear origins, possibly from the Proto-Indo-European *ser-, meaning to bind together; a psychopomp, god of thieves, language, and travel
Hypnos - Ὕπνος, from the Ancient Greek ῠ̔́πνος, meaning both sleep and death; the god of sleep, twin brother to Thanatos
Keres - Κῆρες, literally death spirits; the goddesses of violent death
Lampades - Λαμπάδες; nymphs of the underworld, torch bearers. known in Latin as the nymphae Avernales, or infernal nymphs
Macaria - Μακαρία, literally meaning blessing; the goddess of blessed death
Persephone - Περσεφόνη, likely from a combination of the following Proto-Indo-European terms: *pers-o- (grain, seed) *gʷʰn̥-t- (to destroy, related to Ancient Greek φόνος, which is murder or slaughter) and the feminine suffix *-ih₂; wife of Hades, goddess of spring and the underworld
Styx - Στύξ, related to the Ancient Greek στυγνός, meaning hated, gloomy, hostile; one of the rivers of the underworld, also the goddess of hatred
Tartarus - Τάρταρος, the netherworld and the god of the deepest depths of the underworld
Thanatos - Θάνατος, from the Ancient Greek literally meaning death or corpse, related to the verb θνῄσκω, meaning I die; the god of death, spirit of personified death. twin brother to Hypnos