Sometimes a species got described independently by two or even more authors, either in the same genus or in different genera. To avoid confusion, the International Rules of Zoological Nomenclature regards only the first published name as valid, (principle of priority) all other names hence are synonyms. If the taxa (species) do have each their own type specimen(s), they are regarded as subjective synonyms. If two or more scientific names for a species are based on the same type specimen(s) one will speak of objective synonyms. «. This usually is the result of shifting a taxon in a different genus, if e.g. a new genus was established. In such a case the species name (second name) has to be remained and the name of the author, together with the year of publication be put between brackets.

Subjective synonyms result when two or more species ought to be united because other authors had overlooked that there existed already a description of the animal they assumed to be a new one. Objective synonyms result from the necessity to split an existing genus in two or more new ones. In such a case the species-name ought to be retained and the name(s) of the first author(s) must be put between brackets. E.g. Marcusenius cyprinoides (Linné, 1758) originally was designated as Mormyrus cyprinoides Linné, 1758 and only by Gill, 1862 put into Marcusenius when this new genus became established.

Alternative form for synonymy : synonyms.