† protohaloidadj.Obsoleterare designating a salt formed by the reaction of an acid of a halogen, e.g. hydrochloric acid, with the protoxide of a metal; cf. haloidadj.
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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.