I have always wondered how the X-Men got their name. Is it because of Prof. *X*aviers' starting letter? or maybe because they are *x*tremely cool ;). Any thoughts and/or proofs?
Xavier spent months recruiting his early students (code-named Cyclops, Iceman, Angel, Beast and Marvel Girl), dubbing them "X-Men" because each possessed an "extra" ability normal humans lacked.
Scoping it within the limits of the X-Men movies, specifically X-Men: First Class we have the following
And then later on with MacTaggert,
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.