Please note: Latin Declension Rules"The Third Declension is in a sense a catch-all for various stem-types, and can be very confusing" according to William Harris.
Nouns can be masculine, feminine, or neuter in gender and they may have a consonantal or -io stem. Among the cononantal stems, it may take some practice to figure out where to add the endings, although, the dictionary form should make this clear. Sometimes the root vowel appears to change, as in our second paradigm word below, opus, operis, n.
First, here are the consonantal endings.
The endings of the Third declension are:
singular
nominative -/-
genitive -is/-is
dative -i/-i
accusative -em/-
ablative -e/-e
plural
nominative -es/-a
genitive -um/-um
dative -ibus/-ibus
accusative -es/-a
ablative -ibus/-ibus
Using rex, regis, m. (king), here is the paradigm:
singular
plural
Using opus, operis n. (work), here is the paradigm:
singular
plural
Some nouns of the third declension are called i-stem nouns. They have a genitive plural ending in -"ium." A neuter i-stem noun, animal, animalis (animal), looks a little different from other neuter 3rd declension nouns in the plural because of the "i" which makes the nominative and accusative plural of animal: animalia. The word for sea, mare, maris, is another neuter i-stem noun. Hostis, hostis is a generally masculine i-stem noun.
You would decline the name of Caesar thus:
Caesar, Caesaris, Caesari, Caesarem, Caesare.
Please note: Latin Declensions
