Declension tables

res, rei (f) - thing
Case sing. pl.
Nom. res res
Acc. rem res
Gen. rei rerum
Dat. re rebus
Abl. re rebus

Other examples of fifth declension nouns include dies (day), fides (trust, faith), spes (hope).

They are all feminine except for dies and compounds with dies.

Note with res that it is often found in the compound res publica (republic). This can be written as two words or one, but both parts decline:

Case sing.
Nom. res publicam
Acc. rem publicam
Gen. rei publicae
Dat. re publicae
Abl. re publica