Another wonderful site is http://www.etymonline.com/index.php . I used it a whole bunch to make sure the words I used in my historically based screen play ("Reflections in an Hourglass") were actually in use before 1530. I know that seems a bit picky to some folks but I am careful when I write to make damn sure that the story and background fits. For those who want to be really careful that your story (even fiction stories) does not use words that post date your story, this web site is wonderful.