While terms such as "Earth deity" or Earth mother have sweeping implications in English, the words khthonie and khthonios had a more precise and technical meaning in Greek, referring primarily to the manner of offering sacrifices to the deity in question.
Some chthonic cults practised ritual sacrifice, which often happened at night time. When the sacrifice was a living creature, the animal was placed in a bothros (βόθρος, "pit") or megaron (μέγαρον, "sunken chamber"). In some Greek chthonic cults, the animal was sacrificed on a raised bomos (βωμός, "altar"). Offerings usually were burned whole or buried rather than being cooked and shared among the worshippers.
The myths associating the underworld chthonic deities and fertility was not exclusive. Myths about the later Olympian deities also described an association with the fertility and the prosperity of Earth. Thus Demeter and Persephone both watched over aspects of the fertility of land, yet Demeter had a typically Olympian cult while Persephone had a chthonic one.
Also, Demeter was worshipped alongside Persephone with identical rites, and yet occasionally was classified as an "Olympian" in late poetry and myth. The absorption of some earlier cults into the newer pantheon versus those that resisted being absorbed is suggested as providing the later myths.
The categories Olympian and chthonic were not, however, completely separate. Some Olympian deities, such as Hermes and Zeus, also received chthonic sacrifices and tithes in certain locations. The deified heroes Heracles and Asclepius might be worshipped as gods or chthonic heroes, depending on the site and the time of origin of the myth.
Moreover, a few deities are not easily classifiable under these terms. Hecate, for instance, was typically offered puppies at crossroads—a practice neither typical of an Olympian sacrifice nor of a chthonic sacrifice to Persephone or the heroes. Because of her underworld roles, Hecate is generally classed as chthonic.
As well, the chthonic has connotations with regard to gender, in cultural anthropology; del Valle's Gendered Anthropology describes there being "male and female deities at every level... men associated with the above, the sky, and women associated with the below, with the earth, water of the underground, and the chthonic deities." This was by no means universal; in Ancient Egypt the main deity of the earth was the male god Geb, his female consort was Nut, otherwise known as the sky. Greek mythology likewise has female deities associated with the sky, such as Dike, goddess of justice who sits on the right side of Zeus as his advisor, and Eos, goddess of dawn—and Hades as god of the underworld.
The term Allochthon in structural geology is used to describe a large block of rock which has been moved from its original site of formation, usually by low angle thrust faulting. From the Greek "allo" meaning other and "chthon" designating the process of the land mass being moved under the earth and connecting two horizontally stacked décollements and thus "under the earth".
^Chthonios, Henry George Liddell, Robert Scott, A Greek–English Lexicon, at Perseus.
^"The sacrifice for gods of the dead and for heroes was called enagisma, in contradistinction to thysia, which was the portion especially of the celestial deities. It was offered on altars of a peculiar shape: they were lower than the ordinary altar bomos, and their name was ischara, 'hearth'. Through them the blood of the victims, and also libations, were to flow into the sacrificial trench. Therefore they were funnel-shaped and open at the bottom. For this kind of sacrifice did not lead up to a joyous feast in which the gods and men took part. The victim was held over the trench with its head down, not, as for the celestial gods, with its neck bent back and the head uplifted; and it was burned entirely." (Source The Heroes of the Greeks, C. Kerenyi pub. Thames & Hudson 1978).