Using a fictional race in the name of your website, is that copyright infringement?

If you want to use the word "Na'Vi" in the name of your website, can Cameron's clan come back and sue you, or whoever it is that owns the rights to the word Na'Vi? I know that company names and logos are trademarked and copyrighted, but can you do that with a fictional race like Na'Vi or Klingon or whatever? Where could I go find out if "Na'Vi" is copyrighted? Any advice?