There are third declension nouns in the masculine and feminine with an i stem that have the same number of syllables in the genitive as in the nominative.

Here are the endings for the nouns in the singular:

N : –

G : –is

D : –ī

Acc : –em or –im

Abl : –e or –i

Here are the endings for the Latin word for stream in the singular:

N : amnis

G : amnis

D : amnī

Acc : amnem

Abl : amne or amni