Article 53. Definitions of homonymy in the family group, genus group and species group.
53.1. Homonyms in the family group. In the family group, two or more available names having the same spelling or differing only in suffix [Art. 29.2] and denoting different nominal taxa are homonyms.
Examples. The family-group names METOPIINAE Foerster,  (Hymenoptera; type genus Metopius Panzer, 1806), METOPIINI Raffray, 1904 (Coleoptera; type genus Metopias Gory, 1832) and METOPIINI Townsend, 1908 (Diptera; type genus Metopia Meigen, 1803) are homonyms. (Their homonymy was removed by the Commission emending the spellings of the latter two family-group names to METOPIASINI and METOPIAINI [Opinion 1772, 1994]).
53.2. Homonyms in the genus group. In the genus group, two or more available names established with the same spelling are homonyms.
Example. The generic names Noctua Linnaeus, 1758 (Lepidoptera) and Noctua Gmelin, 1771 (Aves) are homonyms.
53.3. Homonyms in the species group. Two or more available species-group names having the same spelling are homonyms if they were originally established in combination with the same generic name (primary homonymy), or when they are subsequently published in combination with the same generic name (secondary homonymy) (for species-group names combined with homonymous generic names see Article 57.8.1).
Example. Cancer strigosus Linnaeus, 1761 and Cancer strigosus Herbst, 1799 were established for different nominal species in the nominal genus Cancer Linnaeus, 1758, and the specific names are therefore primary homonyms. For an example of secondary homonymy see Article 57.3.1.
53.3.1. The variant spellings of species-group names listed in Article 58 are deemed to be identical spellings for the purposes of the Principle of Homonymy.