What is the noun-forming suffix of word violin?

The word "violin" doesn't have a noun-forming suffix. It's a borrowed word from Italian, where it is "violino".

Here's why:

* Suffixes are added to the end of a word to change its meaning or function. "Violin" is a complete word in its own right, even in Italian.

* The "-in" ending in "violin" is part of the original Italian word. It doesn't have a separate meaning or function in English.

Therefore, "violin" is a noun on its own, and the "-in" is simply part of the word's original form.