Chthonic
adj.  /’kθɒnɪk/
Of or relating to the underworld.
From the Greek chthonius (in/beneath the earth), from chthÅn (earth).
**
Appropriately enough for an adjective pertaining to the underworld, ‘chthonic’ is capable of provoking fear at first glance: like phthonos, syzygy, Houellebecq or Llanfairpwllgwyngyllgogerychwyndrobwllllantysiliogogogoch, it can seem unpronounceable to the unwary English speaker.  To make things still more complicated, the pronunciation depends which side of the Atlantic you’re on. Most British English speakers will pronounce the initial ‘k’ sound, whereas most American speakers leave it silent, like the ‘k’ in ‘knight’ or the final ‘m’ in ‘Mitt Romney is a Mormon’.
Chthonic can be traced directly back to the Ancient Greek chthÅn/khthon (in which, if it helps, the initial ‘k’ sound was definitely pronounced). Ancient Greek was richer than modern English in words for ‘earth’ (and ‘love’):  chthÅn referred to the deities beneath the surface of the ground, while gaia referred to Earth itself. Imagine David Lynch’s opening sequence to Blue Velvet, the sudden plunge from manicured lawn on perfect summer’s day to the voracious insects in the darkness beneath, as a plunge from gaia to chthÅn. From the same Greek root, we get the noun autochthon and the adjective autochthonous, both referring to a native inhabitant of an area.
It should surprise no one to discover that a word with roots in the underworld is used primarily by sci-fi and horror writers today. In its entry for chthonic, Michael Quinion’s World Wide Words blog cites Anthology, Piers Anthony’s first collection of short stories:
Like the rumble of a volcano it came, throbbing up from the fundament, pressuring chthonic valves, gathering into an irresistible swell.
Chthonic also happens to be the name of Taiwan’s foremost metal band (when not clad in corpse paint, lead singer Freddy Lim’s other job is Chairman of the Taiwanese branch of Amnesty International), and serious horror fans should quickly make the connection between chthonic and H.P. Lovecraft’s Cthulhu mythos. Cthulhu, a monster/deity with claws, wings and the head of an octopus, first appeared in The Call of Cthulhu, published in 1928. The lazily-spelt Call of Ktulu is the title of an instrumental on Metallica’s album Ride The Lightning, while Cthulhu Dawn was recorded by Suffolk pseudo-satanists Cradle of Filth in 1999.
Not that you have to dress in leather and wear corpse paint to know what chthonic means… Camille Paglia tried to claim the word for feminist literary theory in Sexual Personae. Reviewing the book for The New Criterion, Roger Kimball defined ‘the chthonic’ as ‘that anonymous, primevally generative impulse out of which life endlessly arises and back into which it ineluctably sinks.’ According to Kimball, Paglia’s use of chthonic echoes the writing of the pioneering Hellenist/feminist/linguist Jane Harrison.
Jung, too, wrote (in English translation) of the ‘chthonic spirit’, which ‘manifests itself as a spirit of evil, as a drive to destroy.’ Jung’s chthonic spirit is close to what Freud described in German as ‘das Es’ (‘the it’), the term which has passed into English as the Id due solely to an over-elaborate translation from James Strachey.
More recently, the Canadian poet David Zieroth mentions rats ‘unleashed from the mocking chthonic gods’.  Andrew Norton, the (on and off) narrator of Iain Sinclair’s Dining on Stones, describes a ‘caduceus tie-pin’ left to him by his great-grandfather: ‘Was this miraculous survivor, Babylonian fragment among craters and future walkways, a Crowleyite token from the chthonic city?’
‘Crowleyite’ points in the direction of Aleister Crowley, the occultist who feuded with W.B. Yeats, a fellow member of the Hermetic Order of the Golden Dawn. Crowley was a part-time poet (translated into Portuguese, following a lengthy written correspondence, by Fernando Pessoa) but is now remembered for founding his own religious order (making sure to include large numbers of female ‘sex magick practitioners’) and calling himself ‘The Great Beast 666’. Crowley’s occultism has been described in numerous books, including — to bring things full circle — Vadge Moore’s recent Chthonic: Prose & Theory. Vadge Moore is, unsurprisingly, a nom de plume: the man behind the pen-name is Tim Madison, a member of Atlanta-based band Chthonic Force.