frenetic (adj.)
late 14c., from Old French frenetike, from Latin phreneticus "delirious," alteration of Greek phrenitikos, from phrenitis "frenzy," literally "inflammation of the brain," from phren "mind, reason" (from PIE *gwhren- "to think") + -itis. The classical ph- was restored mid-16c. Related: Frenetically.