First declension nouns are usually feminine like queen (rēgīna) and widow (vidua). However there is the rare case where masculine nouns like farmer (agricola) and sailor (nauta) also fall under first declension nouns. Here are the singular first declension endings:

Nominative: –a

Genitive: –ae

Dative: –ae

Accusative: –am

Ablative: –ā

Here are the first declension singular forms of the Latin word for lady:

Nominative: domina

Genitive: dominae

Dative: dominae

Accusative: dominam

Ablative: dominā

Here is another example of the first denclension singular word for sailor:

Nominative: nauta

Genitive: nautae

Dative: nautae

Accusative: nautam

Ablative: nautā

Note: the singular first declension of the genitive and the dative are the same.