Someone who has a way with words/uses big words.
Can anyone help?
A person who uses big words is a sesquipedalianist.
See also: http://dictionary.reference.com/search?q=Sesquipedality
A person having a way with words would be eloquent. Not sure what noun could be used to discribe him/her though.
Have you ever thought of the inherent irony of calling someone a sesquipedalianist? I have been called a self-aggrandizing pedantic gasbag on more than one occasion and I thought that was a very effective description.