Psychedelic (psychotomimetic, hallucinogen): 1. (..)pertaining to a change in the normal state of conciousness, usually with some accompanying changes in the acuity of the senses. Also, "mind-manifesting".
2. (..) A drug that can allow such changes to occur. The word was coined by Dr. Humphrey Osmond in the 1950's.
Shulgin, Thikal Transform Press
The "Classic" psychedelics are: LSD, mescaline and psilocybin. Other psychedelics include: 2-CB, 2-CT-2 and 2-CT-7.