Should be a word

I often hear words that I'm sure that people just made up, like conversate. You can say it like it's a word, but that doesn't make it a word. However, I was shocked to learn that there is a word that I've been using that is in fact not a word: themself. Themselves is a word, but the singular of themselves is they. Themself, should be a word but isn't.

Update: The spell-checker is giving me problems with the word conversate, I knew it wasn't a word. I knew it! The spell-checker also won't recognize the word spellchecker, but it does fine with quoizel lighting.