thumb|right|[[Ball-and-stick model of the octadecahedral closo-undecaborate ion, [B11H11]2−, as found in the crystal structure of the benzyltriethylammonium salt.]]
thumb|right|[[Ball-and-stick model of the octadecahedral closo-undecaborate ion, [B11H11]2−, as found in the crystal structure of the benzyltriethylammonium salt.]]
In geometry, an octadecahedron (or octakaidecahedron) is a polyhedron with 18 faces. No octadecahedron is regular; hence, the name does not commonly refer to one specific polyhedron.
Discovered by embedding cosine similarity (sentence-transformers MiniLM, 384-dim).