Magic!

The decline of classical learning and of religious knowledge continues apace. It’s beginning to make me feel quite elderly.

I’m grateful to Martyn Johnson of the University of Cambridge Computer Laboratory for a sound clip from BBC Radio Cambridgeshire.
The newsreader announces a new carol by John Rutter, The Carol of the Magi. But she confidently pronounces Magi as ˈmɑːʒiː. The presenter then thanks her for setting him right on how to pronounce this difficult word, because he is about to interview the composer. (“That’s why you’re a newsreader.”) Fortunately a third person then intervenes to tell them that it should actually be ˈmeɪdʒaɪ.
We’d better not speculate on which language the newsreader thought Magi comes from, or in which language the reading rules for this sequence of letters would produce ˈmɑːʒiː. I bet she doesn’t know what it means, either, or why it/they would have a carol named after it/them.
The Magi are better known as the Wise Men, or the Three Kings, who in the Christmas story brought gold, frankincense and myrrh to give to the baby Jesus.

The word is (as I’m sure you know) the Latin plural of magus, which means a learned man or magician, originally one from Persia. You will also know, although the newsreader probably wouldn’t, that The Magus is a rather well-known novel by John Fowles, later made into a film.
Although in Latin măgus, măgī has a short vowel in the first syllable, its English pronunciation reflects the traditional developments affecting other long-established Latin borrowings: the vowel in an open syllable lengthens and undergoes the Great Vowel Shift, while in the plural Velar Softening changes g to dʒ.
The Romans took the word from the Greeks (Μάγος, pl. Μάγοι), who in turn took it from the Persians. Herodotus tells us of wise men (μάγοι) in Persia who interpreted dreams. According to Wikipedia they were followers of Zoroaster.
The Greeks later widened the meaning of the word to denote any kind of enchanter or wizard, and created a derived verb μαγεύω (classical magéuō, modern maˈʝevo) ‘bewitch, enchant, charm’ and an adjective μαγικός magikós. The latter is the source of our word magic.
According to Wikipedia,

Victor H. Mair provides archaeological and linguistic evidence suggesting that Chinese wū (巫 "shaman; witch, wizard; magician", Old Chinese *myag) was a loanword from Old Persian *maguš "magician; magi".

The word Magi has been in English for around eight hundred years.