Analyzing Everyday Rhetoric: Pondering the English Language

Why is it that in the word “nihil”, the “ni” is pronounced “nee”, but in the words “nihilism” and “nihilistic”, the “ni” is pronounced “ny”? And why is it that in the word “nihilist”, the “ni” can be pronounced either “nee” or “ny”?

The English language is a beautiful, strange, and confusing thing.