Is it memento mor-EE or memento mor-EYE?
Thanks in advanced!
I’d say meMENto MOree, but I’m Spanish… y’all begin by separating the syllables in different spots.
I can’t think of a single word in the English-speaking world that ends in consonant-i, which is pronounced with an “eye” sound. And certainly stuff that is originally Latin should never be pronounced like that.
memento mor-EE - or more correctly - mementå mår-EE as the o is pronounce more like the scandinavian å-sound (as you would pronounce the o in or). (At least, that is what my little book on latin tells me 
)
It depends on what Latin pronunciation you want to use. There are several of them.
Useful datum: the rhymed quatrain with which Wilfred Owen ended his WWI protest poem “Dulce et Decorum Est”:
“My friend, you would not tell with such high zest
To children ardent for some desperate glory,
The old Lie: Dulce et decorum est
Pro patria mori.”
I can: cacti (pl. of cactus).
Not only that, but fungi, syllabi, etc. It’s not all that uncommon under the Traditional English pronunciation of Latin
As a rough guide, if a Latin word has been adopted into English and ends in “i”, the last letter is usually sounded like “eye”. So, that applies to plurals like cacti and fungi as people have said. It also applies to non-plurals like alibi (which just means “somewhere else”).
Like all rules, this has exceptions.
However, if you are quoting a Latin phrase, the English language convention is usually to treat it as a foreign language. We don’t do that very well, but we do pronounce the final “i” as “ee” instead. So in the phrase “memento mori”, the convention is to pronounce it “ee”.
Similarly, many people know that “e.g.” is short for exempli gratia (for the sake of example) and the i in each word is normally pronounced “ee”. Same with “veni, vidi, vici” (I came, I saw I conquered), although we should probably pronounce it “way-nee, weedy, weaky”.