Why is X the unknown?

Here is a link to a video I saw a couple of months ago which really impressed me, so I felt the need to share it. The speaker, Terry Moore, seems like a fascinating guy- not only did he learn Arabic from scratch whilst in his 40's, but it helped him to provide an explanation for a concept we all take for granted: Why is it the letter ‘X’ represents the unknown?

We use X fairly often in everyday speech, which when you think about it, are all used to explain an unknown.

For example:

      -X in mathematics and algebra. Find X. Which always reminds me of this...

     -X-rays, so called because Wilhelm Rontgen (discoverer) did not know what they were.

     -X marks the spot. X is often used to depict the supposed location of an unknown hidden treasure.

     -The X Files: American TV show based around unsolved FBI cases involving unknown paranormal phenomena.

     -Malcolm Little changed his name to Malcolm X to represent his true African family name that he never knew.

     - You could maybe even claim that X as the unknown is responsible for the coining of the word ‘extra’ which goes on to form words such as extraterrestrial which has connotations with the term UFO (Unknown Flying Object)*. 

The video is also relevant for today’s post as he explains Spain’s involvement in the formation of this usage of X and as I’ve just returned from Spain it’s fairly apt!

Give the video a try, it might seem boring but I promise you will learn something! If you don’t watch the video, at least skip to the end, at 3:34 when he provides the short version of why we use X when talking about an unknown thing. 

(This is just an idea I postulated, no idea if there’s any proof behind it).