You can tell what declension a Latin noun is by looking at the noun's genitive singular form.
Third declension.
The Latin noun Homo, hominis is in the third declension.
The Latin word cīvitās in the nominative case, cīvitātis in the genitive, is a third declension feminine noun.
Each latin noun has five forms referred to as declension.
Luna means "moon" in Latin. It is a first declension feminine noun.
"Beef" in Latin is the 1st-declension feminine noun bubula.
Argicola, agricolae, feminine, a first declension noun.
Rebellionis - masculine noun, lll declension
'officina, officinae'. It is a first declension noun.
Hortus is a noun of the second declension in Latin. It is masculine and means "garden." The genitive form is "horti," which is used to indicate possession. As a second declension noun, it follows the typical endings for that category.
'Forum' (a neuter, 2nd declension noun) is used in Latin for "marketplace."
arbor, arboris. It is a 3rd declension noun.