1. [adj]  of a mental state characterized by intense and distorted perceptions and hallucinations and feelings of euphoria or sometimes despair; "a psychedelic experience"
2. [adj]  having the vivid colors and bizarre patterns associated with psychedelic states; "a psychedelic painting"
3. [adj]  producing distorted sensory perceptions and feelings or altered states of awareness or sometimes states resembling psychosis; "psychedelic drugs like psilocybin and mescaline"

PSYCHEDELIC is a 11 letter word that starts with P.