I have always wondered how the X-Men got their name. Is it because of Prof. Xaviers' starting letter? or maybe because they are xtremely cool ;)
Any thoughts and/or proofs?
As stated in X-Men #1;
Xavier spent months recruiting his early students (code-named Cyclops, Iceman, Angel, Beast and Marvel Girl), dubbing them "X-Men" because each possessed an "EX-TRA" ability normal humans lacked.
Scoping it within the limits of the X-Men movies, specifically X-Men: First Class we have the following on the movie's IMDB Quotes page:
Raven Darkholme: We have to call him, Havok. That's his name now. And we were thinking...
[points to Charles]
Raven Darkholme: ...you should be Professor X...
[points to Erik]
Raven Darkholme: ...and you should be Magneto.
Erik Lehnsherr: Exceptional.
And then later on with MacTaggert;
Dr. Moira MacTaggert: You know, one day the government is going to realize that how lucky they were to have Professor X on their side.
Professor Charles Xavier: I suppose I am a real professor, aren't I? Next thing you know, I'll be going bald. We're still on the government side, Moira. We're still G-Men. Just without the "G".
Dr. Moira MacTaggert: No. You're your own team now. It's better. You're X-Men.
Professor Charles Xavier: Yes, I like the sound of that.
So within the scope of the movie, Professor Charles got the idea from MacTaggert and she got the idea from Raven. Though this is not correct within the comics, this is how it is played out within the movie.
They are called X-MEN for two reasons.1) they have a extra chromosome which gives them their abilities, and because of Professor Xavier.