Emily Dickinson Lexicon

HY'SOP, or HYS'SOP, n. [hy'sop; L. hyssopus; Gr. υσσωπος. It would be well to write this word Hysop.]

A plant, Hyssopus officinalis. The leaves have an aromatic smell, and a warm pungent taste. Something called Hyssop was much used by the Jews in purifications. Encyc.