ˌperəˈdinēəm noun
Etymology: New Latin, from Greek peridinēs whirled around (from peridinein to whirl around, from peri- + dinein to whirl, rotate) + New Latin -ium; akin to Greek dinos rotation, whirling — more at dino-
1. capitalized : the type genus of Peridiniidae comprising marine and freshwater dinoflagellates that are typically subspherical to ovoid in outline and that sometimes have the test prolonged into short horns — compare ceratium
2. plural peridiniums -ēəmz or peridinia -ēə : any flagellate of the genus Peridinium