tet·ra·he·dron
noun/ˌtetrəˈhiːdrən/
/ˌtetrəˈhiːdrən/
(geometry)- a solid shape with four flat sides that are triangles
enlarge image四面体 Word Originlate 16th cent.: from late Greek tetraedron, neuter (used as a noun) of tetraedros ‘four-sided’.