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 / ~ī ‡²||–||-um|
- ‡¹ In antique Latin, by words ending in ius or ium the ius/ium became ī in genitive singular. E.g. in antique times, fīlius became fīlī (later and nowdays fīliī) and negōtium became negōtī (later and nowadays negōtiī) in genitive singular.
- ‡² * By words ending in ius the ius becomes ī. E.g. fīlius becomes fīlī in vocative singular.
- The singular vocative of second declension -us nouns is the only place in pure Latin words in which the vocative ever differs from the nominative forms: -e instead of -us. The plural vocative is the same as the nominative. As seen in filius, filiī, the vocative singular changes the -ius into an -ī, instead of changing the -us into an -e.
- deus, -ī m has several irregular plural forms.
|Case||-os / -us m/f||-on / -um n|
|nominative||-os / -us||-on / -um|
|accusative||-on / -um|
|vocative||-e||-on / -um|
- Genitive, dative, ablative, locative and 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.