† proto-combinationn.Obsoleterare the combination of a metal with an electronegative element, radical, etc., such that the electronegative species occurs in the smallest possible proportion.
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1854 J. Scoffern in Orr's Circle Sci., Chem. 436 In almost every case..this metal [sc. manganese] will be found in the state of proto-combination,—either as an oxygen salt of the protoxide, or as a protohaloid salt.