Good question. I predicted on a message board a couple years back i believe 'austerity' as the word of the year and it was.
according to - Word of the Year 2010 - Merriam-Webster Online
www.merriam-webster.com/info/10words.htm Austerity
According to
http://www.merriam-webster.com/dictionary/bitcoin does not exist but they do have some suggestions...
bitchin'
biotin
butt in
bichon
biting
button... well you get it.
So, if only Merriam-Webster actually had bitcoin as a word, I would say Bitcoin was the word of the year. Stodgy old Merriam-Webster, they'll be around for the Crowning I'm sure.