Nostradamus was certainly not a prophet by the first definition. But it is asserted by some that he was a prophet who foretold future events. But did he? Prophecies, in order to be verified, must be specific and detailed enough to be undeniably true.
For example, in the Bible, a Messianic prophecy about Jesus the Messiah being nailed by His hands and feet is found in Psalm 22:16, where it prophetically states that "they have pierced my hands and my feet." That was written at a time when crucifixion was not a method of execution in Israel. But that is exactly how Jesus died. There are specific details that are clear and correlate to the fulfillment. There are hundreds and hundreds of such detailed prophecies about Jesus’ first advent, all of which came true.
But Nostradamus did not have this kind of detail in his prophecies. For example, this prophecy of Nostradamus is believed by some to foretell the 9/11 attacks:
"In the year of the new century and nine months, From the sky will come a great King of Terror. The sky will burn at forty-five degrees. Fire approaches the great new city."
The problems with this “prophecy” are numerous. First, statements in different writings from Nostradamus had to be compiled to create this four-statement section. Second, who is the King of Terror coming from the sky, and how does that relate to the airplanes that flew into the buildings? Third, how does the sky burning at forty-five degrees relate to the burning of buildings? Finally, in no way can New York City be described as a “new city” in 2001. It is, in fact, one of the oldest cities in the country.
The extreme vagueness of the prediction, coupled with the application to things that aren’t clearly being spoken of, is called "retroactive clairvoyance." This is when something written beforehand needs to be changed and the modern event squeezed into a very vague and unspecific statement. Nostradamus' prophecies all fit into this category.