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Beginners' Latin
King (Henry IV), historiated initial. c.1402. Cat ref: DL 42/1 f 51. Copyright of the Chancellor and Council of the Duchy of Lancaster

Lesson 7: Third declension nouns and adjectives

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Third declension nouns

You can identify third declension nouns by their genitive singular ending ‘-is’.

You cannot identify third declension nouns in the nominative because they

  • Have various forms and spelling
  • Have endings that do not reveal their gender
  • Can be masculine, feminine or neuter

To decline a third declension noun:

  • Find the genitive singular, which will end ‘-is’
  • Remove the ‘-is’, leaving you with the stem
  • Add the endings shown below

Endings for Masculine and Feminine nouns

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Case Singular Plural
Nominative various -es
Vocative same as nominative -es
Accusative -em -es
Genitive -is -um
Dative -i -ibus
Ablative -e -ibus

Look at our example of rex, regis (m.) king

Case Singular Plural
Nominative rex reges
Vocative rex reges
Accusative regem reges
Genitive regis regum
Dative regi regibus
Ablative rege regibus

Endings for Neuter nouns

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Case Singular Plural
Nominative various -a
Vocative same as nominative -a
Accusative same as nominative -a
Genitive -is -um
Dative -i -ibus
Ablative -e -ibus

The genitive, dative and ablative endings are the same as for rex.

Handy hints Remember
nominative and accusative cases of neuter nouns are always the same. The plural always ends in ‘a’.

Look at our example of jus, juris (n.) law, right

Case Singular Plural
Nominative jus jura
Vocative jus jura
Accusative jus jura
Genitive juris jurum
Dative juri juribus
Ablative jure juribus

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Common third declension nouns:

abbas, abbatis (m.) abbotGlossary - opens in a new window
etas, etatis (f.) age
executor, executoris (m.) executorGlossary - opens in a new window
heres, heredis (m., f.) heir
homo, hominis (m.) man
miles, militis (m.) knightGlossary - opens in a new window
pater , patris (m.) father
uxor , uxoris (f.) wife

You need to know the genitive case of a third declension noun, in order to decline it.
Therefore, both the nominative and genitive forms are provided in full in this tutorial.

curia domini Regis the court of the lord king
Gregorius Basset et Johanna Hastings executores Willelmi Stuart sunt Gregory Basset and Joanna Hastings are the executors of William Stuart

These personal names decline like third declension nouns:

Agnes, Agnetis (f.) Agnes
Johannes, Johannis (m.) John
Mathildis, Mathildis (f.) Matilda
Simo, Simonis (m.) Simon

predictus abbas Johannes hoc manerium tenet The aforesaid Abbot John holds this manor.
Simo filius et heres predicte Agnetis est et etatis decem annorum est Simon is the son and heir of the aforesaid Agnes and is [of] the age of ten years.

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A phrase that you will often see at the beginning of royal documents is

Willelmus dei gratia rex William by the grace of God king gratia, -e (f.) grace
Maria dei gratia regina Mary by the grace of God queen  

ego Johannes dei gratia rex terram abbati Simoni hac carta do et confirmo I, John, by the grace of God king, give and confirm the land by this charter to Abbot Simon  

Genitive plural '-ium'

Some third declension nouns end ‘-ium’ in the genitive plural.

For example pars, partis (f.) part; civis, civis (m.) citizen

summa partium the sum of the parts summa, -e (f.) sum

These and other irregular nouns are noted in the grammar table Grammar table - opens in a new window and wordlistWordlist - opens in a new window.

Checklist Checklist:
Are you confident with:
The genitive singular ending of third declension nouns?
How to decline rex?


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