tetrahedro-

https://doi.org/10.1351/goldbook.T06290
An affix used in names to denote four atoms bound into a tetrahedron.
Sources:
Blue Book, p. 465 (https://www.acdlabs.com/iupac/nomenclature/)
Red Book, 3rd ed., p. 245 (https://doi.org/10.1515/pac-2014-0718)