Why is vacuum spelled with two

The word "vacuum" is spelled with two "u"s because it comes from the Latin word "vacuus," meaning "empty" or "void." The Latin word itself contained two "u"s, and that spelling was carried over into English when the word was borrowed.

Here's a bit more about the etymology:

* Latin: "vacuus"

* Medieval Latin: "vacuum" (with the addition of the "m" at the end)

* English: "vacuum"

So, the double "u" is simply a reflection of the word's Latin origins.