From Middle English frantike, frentik, variant of frenetik, from Old French frenetique, from Late Latin phreneticus, alteration of phreniticus, from φρενιτικός (phrenitikós, “mad, suffering from inflammation of the brain”), from φρενῖτις (phrenîtis, “inflammation of the brain”), from φρήν (phrḗn, “the brain”). Doublet of frenetic and phrenitic.