Emily Dickinson Lexicon

PHRE-NI'TIS, n. [Gr. φρενιτις, from φρην, the mind. The primary sense of the root of this word is to move, advance or rush forward; as in L. animus, animosus, and the Teutonic mod, Eng. mood.]

1. In medicine, an inflammation of the brain, or of the meninges of the brain, attended with acute fever and delirium. – Encyc.
2. Delirium; phrensy. [It is generally written in English, phrensy or frenzy.]