Dynastidan \Dy*nas"ti*dan\, n. [Gr. ?, fem. of ?. See {Dynast}. The name alludes to the immense size of some species.] (Zo["o]l.) One of a group of gigantic, horned beetles, including {Dynastus Neptunus}, and the Hercules beetle ({D. Hercules}) of tropical America, which grow to be six inches in length.