Latin fourth-declension nouns — Classical languages, 14–17
You learn to recognise a smaller but important group of Latin nouns whose endings often look different from the patterns you already know. The point is not to memorise a table blindly: it is to identify forms such as manus and understand their job in a sentence.
A noun family with u in its pattern
Fourth-declension nouns often have u as the key vowel in their endings. Manus means “hand”: manus can be “the hand” or “of the hand”, while manum means “the hand” as the object of an action. Their gender is not always predictable, so the dictionary entry matters too.
Why was this pattern needed?
Latin needed a way to mark the jobs of nouns such as manus, exercitus and portus without relying on word order. These words belonged to an older pattern that stayed productive beside the other declensions. The result is useful, but untidy: several forms look alike, so context and agreement must help you.
Reading exercitus
Take the sentence Exercitus urbem oppugnat. First, find exercitus in the dictionary: exercitus, -us, masculine, “army”. Its -us ending can be nominative singular, so it can be the subject. Oppugnat is “attacks”, and urbem is the object: “The army attacks the city.”
Do not trust -us by itself
A reasonable first guess is that every noun ending in -us is a second-declension masculine noun, because servus follows that familiar pattern. But exercitus is different: its genitive is exercitus, not servi, and its dative singular is exercitui. Check the genitive in the dictionary before choosing the declension.
Why it still matters
You meet fourth-declension nouns in Latin texts about armies, harbours, journeys and hands-on actions: exercitus, portus, adventus and manus. They also appear inside modern words such as “advent” and “manual”. Knowing the pattern lets you read a sentence instead of guessing from a familiar-looking ending.
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