Second declension nouns

Second-declension nouns are the second big noun family, marked by the genitive ending -ī. Most are masculine and end in -us (servus, slave; amīcus, friend) or -er (puer, boy), though a smaller group is neuter and ends in -um (bellum, war).

Like all Latin nouns, these change their endings to show their job rather than relying on position. The vowel "o/u" runs through the endings, which is why some books call this the "o-declension."

Case	Singular	Plural
Nominative	servus	servī
Genitive	servī	servōrum
Dative	servō	servīs
Accusative	servum	servōs
Ablative	servō	servīs

Examples:

• Servus dominō pāret. - The slave obeys the master.
• Amīcī puerōrum veniunt. - The boys' friends are coming.

Two watch-points for English speakers. The ending -ī is doing double duty: genitive singular and nominative plural, so read carefully. And beware the pair servō: it serves as both dative ("to the slave") and ablative ("by the slave"), so let the sense of the sentence decide. Do not assume the first -us word is automatically the subject; check whether it might be part of a longer chain.