I used the word 'arbitrarity,' and, in my usual fashion, looked it up to check the spelling & usage. It wasn't there! Merriam-Webster Unabridged Online doesn't mention any such variation of the word 'arbitrary.' However, when I searched google for the word, I could see that its use is widespread (and not just as a misspelled 'arbitrarily'). Any one know the scoop on this word? Is it just a common mistake, or is the dictionary missing something?