Try translating these sentences on your own!

(1) Es amīcus. (amīcus = friend)

(2) Est cervus. (cervus = deer)

(3) Sum medicus. (medicus = doctor.)

The three sentences all contain second declension nouns. The most basic second declension nouns end in -us and are mostly masculine. For the second sentence, you might have translated this sentence as, “He is a deer” but the better translation may be “It is a deer”. Some Latin nouns end in -ius. The third sentence is an example of a second declension noun that ends in -ius.

Now take a look at these sentences:

(1) Sunt servī. (servī = servants)

(2) Sumus dominī. (dominī = masters, lords of the house)

As you can see these second declension nouns in the nominative don’t end in -us, they end in -ī. This is because second declension nouns that end in -us in the plural end in -ī.

Let’s move on to more examples:

(1) Est pinus. (pinus = pine tree)

(2) Sum puer. (puer = boy)

(3) Es vir. (vir = man)

The fist sentence is an example of a second declension noun that is feminine. There are a few feminine second declension nouns, so don’t automatically assume that all second declension nouns are masculine. A general rule of thumb is that nouns that end in -us that are plants, trees or cities, tend to be feminine. The second sentence contains a second declension noun that ends in -er. The third sentence is an example of a second declension noun that ends in -ir. As you can see, you can’t assume that only -us ending nouns are second declension nouns.