Declension of annus

Magister, magistri ...

Magister, magistri

Magister is a second declension noun. Second declension nouns ending in r are declined like this (but see puer) :-

Case Singular Plural
Nom. magister magistri
Voc. magister magistri
Acc. magistrum magistros
Gen. magistri magistrorum
Dat. magistro magistris
Abl. magistro magistris