Most fourth declension nouns are masculine, but there are a few feminine fourth declension nouns.

Here is the singular form of the noun manus (hand)

Nom – manus

Gen – manūs

Dat – manuī

Acc – manum

Abl – manū

Voc – manus

Manus (hand) in the plural:

Nom – manūs

Gen – manuum

Dat – manibus

Acc – manūs

Abl – manibus

Voc – manūs