Overview
The third declension is the largest declension and contains consonant stems, vocal (i-) stems and mixed stems. This revision covers how to recognise each group, with the pure and mixed i-stems, and the fourth-declension nouns that follow in the course.
Vocal (i-stem) nouns
The third declension contains a group of nouns called i-stems.
There are two subcategories of i-stem nouns: pure and mixed.
Pure i-stem nouns include nouns of feminine and neuter gender.
They follow the parisyllabic rule, meaning they have the same number of syllables in the nominative singular and genitive singular.
Mixed i-stem nouns are identified by the double consonant rule.
They include nouns of all three genders (masculine, feminine, and neuter).
Latin feminine i-stems
In medicine, there is a small group of Latin feminine i-stem nouns with limited use.
ravis, is, f - hoarseness
sitis, is, f - thirst
febris, is, f - fever, temperature, pyrexia
febris continua - continued fever
febris curativa - artificial pyrexia
febris flava - yellow fever (jack), black vomit
febris Q - Queensland fever
tussis, is, f - cough
pertussis, is, f - whooping cough
pelvis, is, f - id.
pelvis ossa coxae = os sacrum + os coccygis
pelvis renalis - kidney's pelvis
pelvis angusta - contracted pelvis
pelvis plana - flat pelvis