4th Declension nouns end in –us for both nominative and genitive singular forms.

The declension may look odd, but it is essentially the same as the 3rd Declension, with a dominant u in the stem which consumes most adjacent vowels put next to it (e.g. nominative plural = manu + es = manus).

There are only three 4th Declension nouns to learn at GCSE level.

domus (home) can have the alternative forms domo (dat. sing.), domos (acc. pl.), and domorum (gen. pl.). It also has a locative form domi (at home).