Why is Jesus inflected in such a way?

Question

The name Iesus is declined in a very peculiar way in Latin, and no other word seems to follow similar declensions. Why is this so? Is there a way to put this broader declension in context to make some sense of it and make it easier to remember?

It seems that the Latin declension is borrowed directly from the Greek one. I only know Greek at a very basic level, but the Greek declension looks unusual as well. The word is not originally Greek, but I would have expected a "more Greek" declension for a borrowed word. I realize that this may be ultimately a question about Greek (or yet another language, depending on how far the chain extends), but my sole goal is to understand the Latin word.

Answer 1

'Why' isn't usually a good question for these types of things, because the answer is often "just because." The Greek isn't typical, but it does have a parallel with o-contracted words like νοῦς, περίπλους, or (neuter) κανοῦν.

Nominative  Ἰησοῦς         νοῦς
Genitive    Ἰησοῦ          νοῦ
Dative      Ἰησοῖ/Ἰησοῦ    νῷ
Accusative  Ἰησοῦν         νοῦν
Vocative    Ἰησοῦ          νοῦ

The only part that looks odd is the dative, but that actually has a close precedent elsewhere:

In Greek papyri there is widespread confusion of ε and η and ο and ω reflecting a loss of phonemic distinctions of quantity in koine Greek.

Also, it's not unheard of for Semitic names to come in irregular in the Septuagint (Μωυσῆς).

As for why Latin would have stuck with the Greek, well, they tended to. Plenty of names that are indeclinable in the LXX or NT were likewise left without endings in the Latin translations. Sacred scripture also adds a familiarity and conservatism to language that makes it nigh impervious to some forms of change, which is why English contains Hebraisms (e.g. [2]; see [1]).