Declension of Greek nouns in Latin

Greek Substantives, especially proper names, are commonly Latinized, and declined regularly according to their stem-characteristics. Many Substantives, however, either retain their Greek forms exclusively, or have the Greek and Latin forms side by side. These variations occur principally in the Singular, in the Plural the declension is usually regular. Note, however, that many Greek names, of the third declension in Latin, pass over into the first declension in the Plural; as, Thūcȳdidās, Hyperīdae, and many names in -crates (such as, Sōcratae as well as Sōcratēs).

In the Vocative Singular, Names in -is, -ys, -ēs, -eus and -ās (Gen., -antis) form the Vocative by dropping the s from the Nominative.

In the Accusative Singular, many Proper and some common nouns, imparisyllabic, often take the Greek -a for -em. Names in -ēs, is and ys take -ēn, -in and -yn as well as -ēm, -im and ym.

A few Greek nouns in -os, mostly geographical, belong to the second declension, and sometimes make Accusative in -on as Dēlos, Acc. Dēlon (but Dēlum in prose).

In the Genitive Singular, names in -ēs, parisyllabic, take -ī as well as -is. Some Feminine nouns in -ô have Genitive in -ūs.

Greek Names ending in -eus are declined both according to the Greek and according to the Latin Second Declension (but the Genitive -eī and the Dative -eō are often pronounced as one syllable in poets).

In the Nominative Plural, imparisyllabic Nouns often take -es instead of -ēs and, in the Accusative Plural, the same Nouns often take -ā instead of -ēs.

In the Genitive Plural, -ōn and -eōn are found in the titles of books; as, Geōrgicōn and Metamorphōseōn.

Greek Neuter Nouns in -ma (Gen., -matis) always make their Dative and Ablative Plurals in -īs instead of -ibus.