The Stem of nouns of the Fifth Declension ends in ē-, which appears in all the cases. The Nominative is formed from the stem by adding s.
FIFTH DECLENSION (ē-STEMS)
§§95–98 · 4 sections
Nouns of the Fifth Declension are declined as follows:—
| rēs, F., thing | diēs, M., day | fidēs, F., faith |
| STEM rē- | STEM diē- | STEM fidē- |
| SINGULAR | ||||
| CASE-ENDINGS | ||||
| NOM. | rēs | diēs | fidēs | -ēs |
| GEN. | rĕī | diēī (di ē) | fidĕī | -ēī (-ē) |
| DAT. | rĕī | diēī (di ē) | fidĕī | -ēī (-ē) |
| ACC. | rem | diem | fidem | -em |
| ABL. | rē | diē | fidē | -ē |
| PLURAL | ||||
| NOM. | rēs | diēs | -ēs | |
| GEN. | rērum | diērum | -ērum | |
| DAT. | rēbus | diēbus | -ēbus | |
| ACC. | rēs | diēs | ēs | |
| ABL. | rēbus | diēbus | -ēbus |
All nouns of the Fifth Declension are Feminine, except diēs (usually M.), day, and merīdiēs (M.), noon.
Diēs is sometimes feminine in the singular, especially in phrases indicating a fixed time, and regularly feminine when used of time in general: as, cōnstitūtā diē, on a set day; longa diēs, a long time.
The following peculiarities require notice:—
Of nouns of the fifth declension, only diēs and rēs are declined throughout. Most want the plural, which is, however, found in the nominative or accusative in aciēs, effigiēs, ēluviēs, faciēs, glaciēs, seriēs, speciēs, spēs.
The Locative form of this declension ends in -ē. It is found only in certain adverbs and expressions of time:—
| hodiē, to-day; | diē quārtō (old, quārtī), the fourth day; |
| perendiē, day after to-morrow; | prīdiē, the day before. |
The fifth declension is closely related to the first, and several nouns have forms of both: as, māteria, -iēs; saevitia, -iēs. The genitive and dative in -ēī are rarely found in these words.
Some nouns vary between the fifth and the third declension: as, requiēs, satiēs (also satiās, genitive -ātis), plēbēs (also plēbs, genitive plēbis), famēs, genitive famis, ablative famē.