21.11.25: Level 1; Carolus et Maria [16][v] Grammar Notes (1): 4th declension nouns

There are four new nouns introduced in this text, all of which end in -us, but they belong to different declensions.

arcus: bow

carrus: wagon; cart

locus: place

manus: hand

Until now you have seen that nouns ending in -us are 2nd declension, and almost all of them are masculine. However, as mentioned in earlier posts, there are other nouns ending in -us that are not 2nd declension. How can you tell the difference? The answer is – if you only look at the nouns in the way they are listed above – you can’t, which is why it is important to note the nominative and genitive singular of a Latin noun, because the genitive singular is different for each declension i.e. it is the genitive singular that will tell you the declension.

[i] carrus and locus are second declension and are listed as follows:

carrus, -ī (gen. sg. in -ī) [2/m]

locus, -ī (gen. sg. -ī) [2/m]

[ii] arcus and manus are fourth declension and are listed as follows:

arcus, -ūs (gen. sg. in -ūs) [4/m] i.e. the only distinction between the nominative and genitive singular is the vowel length (nom. sg -us; gen. sg. -ūs)

Almost all 4^th declension nouns in -us are masculine, but there are exceptions:

manus, -ūs (gen. sg. in -ūs) [4/f]

Some 4^th declension nouns are neuter and end in a distinctive -ū in the nominative, for example:

cornū, -ūs (gen. sg. in -ūs) [4/n]: horn

LINK to all previous posts on the 4^th declension:

https://mega.nz/file/DA9mFBBY#Yj4KLIjYqE17OtRVQkSaJZqDv6jNyOnfZjGSaIPUsc0