What sound does the Greek letter Ϡ make?

The Greek letter Ϡ (sampi) is not used in modern Greek. It was used in ancient Greek to represent the sound of the letter "s" at the end of a word, and it's pronounced like the letter "s" in the English word "sun".

However, it's important to note that the pronunciation of ancient Greek is not perfectly known, and there is some debate among scholars about how exactly sampi was pronounced.