Entheogens are psychoactive substances that induce alterations in perception, mood, consciousness, cognition, or behavior for the purposes of engendering spiritual development or otherwise in sacred contexts. The anthropological study has established that entheogens are used for religious, magical, shamanic, or spiritual purposes in many parts of the world. Entheogens have traditionally been used to supplement many diverse practices geared towards achieving transcendence, including divination, meditation, yoga, sensory deprivation, healings, asceticism, prayer, trance, rituals, chanting, imitation of sounds, hymns like peyote songs, drumming, and ecstatic dance. The psychedelic experience is often compared to non-ordinary forms of consciousness such as those experienced in meditation, near-death experiences, and mystical experiences. Ego dissolution is often described as a key feature of the psychedelic experience.
The neologism entheogen was coined in 1979 by a group of ethnobotanists and scholars of mythology (Carl A. P. Ruck, Jeremy Bigwood, Danny Staples, Richard Evans Schultes, Jonathan Ott and R. Gordon Wasson). The term is derived from two words of Ancient Greek, ἔνθεος (éntheos) and γενέσθαι (genésthai). The adjective entheos translates to English as "full of the god, inspired, possessed," and is the root of the English word "enthusiasm." The Greeks used it as praise for poets and other artists. Genesthai means "to come into being". Thus, an entheogen is a drug that causes one to become inspired or to experience feelings of inspiration, often in a religious or "spiritual" manner.
Ruck et al. argued that the term hallucinogen was inappropriate owing to its etymological relationship to words relating to delirium and insanity. The term psychedelic was also seen as problematic, owing to the similarity in sound to words about psychosis and also because it had become irreversibly associated with various connotations of the 1960s pop culture.