Dies and the fifth declension

Here are some other fifth declension nouns for practice: effigies, effigiei, f., effigy. fides, fidei, f., faith.
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The Fifth Declension Endings.

1. What is the 5th declension of Latin dies?
2. What is a 5th declension word?
3. Why are there 5 declensions in Latin?

What is the 5th declension of Latin dies?

The word dies is a fifth declension noun and as such is regarded to be feminine. In the order of nominative, accusative, genitive, dative then abalative cases in the singular form, dies declines as follows: dies, diem, diei, diei, die.

What is a 5th declension word?

Latin words of the fifth declension are generally of feminine gender (exceptions are dies and meridies, as well as some Greek proper nouns), end in -ēs with a genitive in -ēī after -i- or in -ĕī after consonant, and have an invariable stem. The plural forms of most fifth declension nouns are uncommon.

Why are there 5 declensions in Latin?

Diēs, for example, became the only masculine in the fifth-declension, while domus can't decide whether it's second or fourth. But almost no nouns actually remained "irregular"; Latin was very good at forcing them into these five categories. And thus, the variety of PIE nouns became Latin's five-declension system.