For Latin nouns ending in -us, which ending is used to form the plural?

For Latin nouns ending in -us, which ending is used to form the plural?

• A. i
• B. a
• C. ae
• D. es

Answer: (A)

In Latin, nouns that end in -us are usually masculine and belong to the second declension. Their plural is formed by replacing -us with -i. This is why you see familiar medical terms in their plural as nuclei, fungi, radii, thrombi, and foci. The pattern -us → -i is the standard plural formation for these nouns. The other endings would fit different noun groups (for example, -a/-ae for many first-declension feminine nouns), so they don’t represent the usual plural for -us nouns.

In Latin, nouns that end in -us are usually masculine and belong to the second declension. Their plural is formed by replacing -us with -i. This is why you see familiar medical terms in their plural as nuclei, fungi, radii, thrombi, and foci. The pattern -us → -i is the standard plural formation for these nouns. The other endings would fit different noun groups (for example, -a/-ae for many first-declension feminine nouns), so they don’t represent the usual plural for -us nouns.