Appendix:Latin second declension
Latin words of the second declension are generally of masculine gender (ending in -us) or neuter gender (ending in -um), and have a genitive in -ī.
Latin words borrowed from Ancient Greek’s second declension are inflected with a varying mixture of Greek and Latin endings.
|Case||-us, -ī (m)||stem in
|-um, -ī (n)|
|vocative||-e / -ī2||–||-um|
1In Archaic Latin, words ending in -ius and -ium take the ending -ī in the genitive singular, e.g. in earlier Roman Republic times, fīlius would change to fīlī in the genitive singular (cf. later and nowadays fīliī), and negōtium would change to negōtī (cf. later and nowadays negōtiī).
2In words ending in -ius the -ius becomes ī, e.g. fīlius becomes fīlī in the vocative singular.
- The singular vocative of second declension -us nouns is the only place in pure Latin in which the vocative ever differs from the nominative: -e instead of -us. The plural vocative is the same as the nominative. As seen in filius, filiī, however, the vocative singular changes -ius and -ium nominative endings into an -ī, instead of changing the -us ending into an -e and the repeating the -um ending.
- deus, -ī m has several irregular plural forms.
|-os/ -us m or f||-on/ -um n|
|nominative||-os/ -us||-on/ -um||-ī||-a|
- Genitive, dative, ablative, locative and usually also the plural are the same as in Latin words; for -os/-us it is like Latin -us and words with stem in r/er, and for -on/-um it is like Latin -um.
- In case of proper nouns and book titles genitive plural -ōn and nominative plural -oe can appear, as in Vergil's Georgicon Libri alias Georgica and in Terence's Adelphoe.