(a) Prefixed to names of binary compounds of elements or radicals, names of salts, etc., to signify four atoms, groups, or equivalents of the element or radical in question; as tetrachloriden. at sense 2a(c)(ii); so tetrasulphide, tetriodide, tetroxiden., tetrahydroxide, tetramethide, tetracetate, tetraphosphate, etc.
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1880 H. E. Roscoe & C. SchorlemmerTreat. Chem. II. ii. 434 Rhodium tetrahydroxide Rh(OH)4..this compound separates out as a green powder.