Early 16th century; earliest use found in John Skelton (c1460–1529), poet. From classical Latin phrenēsis delirium, madness, frenzy from Hellenistic Greek ϕρένησις (as a Greek word in Celsus) from ancient Greek ϕρεν-, ϕρήν mind + -ησις, extended form of -σις, after Hellenistic Greek ϕρενητικός, on the model of pairs of related words in -ησις, -ητικός.