tet·ra·he·dron 
(tĕt′rə-hēdrən)
(tĕt′rə-hēdrən)n. pl. tet·ra·he·drons or tet·ra·he·dra (-drə)
A polyhedron with four faces.
[Greek tetraedron, from neuter of tetraedros, four-faced : tetra-, tetra- + -hedros, sided; see -HEDRON.]
tetrahedron