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Concept Breakdowns

Latin Third Declension Noun Endings

Third declension nouns are among the most challenging in Latin because their nominative singular forms vary unpredictably. Mastering the genitive singular and noun stem is critical for AP Latin, college Latin, and reading Caesar or Cicero confidently.

Interactive Deck

5 Cards
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What defines a third declension noun?

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Third declension nouns have a genitive singular ending in -is. The stem is found by removing -is from the genitive form.

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Third declension masculine and feminine endings

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  • Nom: varies
  • Gen: -is
  • Dat: -ī
  • Acc: -em
  • Abl: -e
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Neuter third declension rule

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Neuter nouns always have identical nominative and accusative forms. In the plural, neuter nominative/accusative ends in -a.

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What distinguishes i-stem third declension nouns?

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How do you find a third declension stem?

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Frequently Asked Questions

How do I find the stem of a third declension noun?

Remove -is from the genitive singular. For example, miles, milit-is gives the stem milit-. Every other case form is built on this stem, so always memorize third declension nouns with both nominative and genitive forms.

What is the difference between i-stem and non-i-stem third declension nouns?

i-stem nouns show -ium in the genitive plural and -ī in the ablative singular, while non-i-stems use -um and -e. i-stems are typically identified by the parisyllabic rule (equal syllables in nominative and genitive) or by having two consonants before -is.

Why do third declension nominative singular forms vary so much?

Third declension nouns descend from many different Proto-Indo-European stem types, so their nominative singulars were never regularized. The genitive singular in -is is the reliable identifier — always learn nouns with both nominative and genitive listed.