As the title suggest, this post will be about third declension nouns with unpredictable endings in the nominative singular.

N : –

G : –is

D : –ī

Acc : –em

Abl : –e

The endings for the Latin word for father.

N : pater

G : patris

D : patrī

Acc : patrem

Abl : patre

The endings for the Latin word for legion.

N : legiō

G : legiōnis

D : legiōni

Acc : legiōnem

Abl : legiōne