 Nouns in "-os" are identical to the Ancient Greek second declension, except for the final "-n" of the accusative singular.However, in other parts of speech that follow the same declension and where clarity is necessary, such as in pronouns, the "-n" is added.When the word has more than two syllables and the antepenult is accented, the accent fluctuates between the antepenult and the penult according to whether the last syllable has one of the ancient long diphthongs, -ου, -ων or -ους.