Language is a living thing so certain types of pronunciation can enter common usage and become accepted as a way of saying something.
Think of Latin which is a dead language. Nobody speaks it anymore outside academic/historical circles. Therefore it no longer grows or changes in the way it is spoken.
There are 2 commonly accepted ways of pronouncing Latin words - ecclesiastical and restored pronunciation. Ecclesiastical is the pronunciation most people are familiar with because it has been preserved by the Christian church long after the fall of the Roman empire. So the way you pronounce "veni vidi vici" in eclesiastical Latin is Ven-ee, Vee-dee, Veetch-ee.
In restored pronunciation it is more like Wen-ee, Weed-ee, Wee-kee.
How do we know this? Because two thousand years ago, people complained about how other people pronounced their words and wrote it down, like how everyone is doing in this thread. We know how it was pronounced before the christian church came along because of really old dead dudes writing big old twit longer rants on parchment and vellum. Then thousands of years later we dug up by the manuscripts.
Both forms of pronunciation are acceptable in the 21st century and it is only wrong if you mix them up. i.e. Ven-ee, Vee-dee, Vee-kee. This is like mixing up the restored hard C and dropping it into church latin where the "C" in Vici is not a "K" sound and more like a "Ch" sound.
But again we can do this because we are talking about Latin as a language that is no longer spoken so it is trapped in a time capsule. Living languages grow and change in use. We form new words and new ways of pronouncing those words.
Latin words can also occur in modern speech as in legal terminology like "Subpoena Duces Tecum" (pronounced Sub-pee-nah Duke-ess Take-um). But since not many people outside the legal profession use legal terminology and are unfamiliar with the accepted ways to pronounce them, lets use words gamers are familiar with like "Natus Vincere" from the e-sports organisation. From the Latin meaning born conqueror/victor (born winner essentially).
In restored pronunciation I would say this as "Nah-toos Win-keh-ray". In the ecclesiastical pronunciation I would say this as "Nah-toos Vin-che-ray". I don't feel like either is wrong.
So Gill-o-teen is an acceptable way to pronounce Guillotine. Gee-uh-teen is also an acceptable way to pronounce Guillotine. Although the English word is derived from the French word which came from a French name.
Most of our English words trace their roots back to Greek or Latin words and over time and distance the pronunciation changes.
For example, the english word "Atrium" pronounced long a (as in cake) "ei-tree-um" from the restored Latin "Atrio" pronounced short a "at-tree-oh".
The modern day Italian pronunciation of atrio is closer to the restored Latin. We brits were further away from the seat of the Roman empire so we bastardized the pronunciation more, since there wasn't enough Romans around to tell us we were wrong. Then we turned into a naval superpower and forced everyone else to speak our (bastardized) words.
dictionary.cambridge.org
