horseradish UK /ˈhɔːsɹædɪʃ/US /ˈhɔɹsɹædɪʃ/ noun3 •A plant of the mustard family, Armoracia rusticana, cultivated for its edible root. •A pungent condiment made from the root of the plant. •(slang) Nonsense. formshorseradishes