"the subculture associated with users of psychedelic drugs; psychedelic phenomena collectively," 1967, from psychedelic + -ia.
Entries linking to psychedelia
psychedelic adj.
occasionally psychodelic, "producing expanded consciousness through heightened awareness and feeling," 1956, of drugs, suggested by British-born Canadian psychiatrist Humphry Osmond in a letter to Aldous Huxley and used by Osmond in a scientific paper published the next year; from Greek psykhē "mind" (see psyche) + dēloun "make visible, reveal" (from dēlos "visible, clear," from PIE root *dyeu- "to shine").
In popular use from 1965 with reference to anything producing effects or sensations similar to the common perception of the effects of a psychedelic drug. As a noun, "a psychedelic drug," from 1956.
-ia
word-forming element in names of countries, diseases, and flowers, from Latin and Greek -ia, noun ending, in Greek especially used in forming abstract nouns (typically of feminine gender); see -a (1). The classical suffix in its usual evolution (via French -ie) comes to Modern English as -y (as in familia/family, also -logy, -graphy). Compare -cy.
In paraphernalia, Mammalia, regalia, etc. it represents Latin or Greek -a (see -a (2)), plural suffix of nouns in -ium (Latin) or -ion (Greek), with formative or euphonic -i-.