Tergiversate is Dictionary.com's word of the year (as opposed to Oxford Dictionaries' word of the year, which was 'squeezed middle'). Tergiversate means to equivocate or 'to change repeatedly one's attitude or opinions with respect to a cause or subject', as Dictionary.com's own website explains. I prefer the OED's definition myself, "To practise tergiversation; to desert one's party, turn renegade, apostatize; to shift, shuffle, use subterfuge or evasion; to refuse to obey, act the recusant". The word is pronounced with the stress on the first syllable, and with the g pronounced as a j, as in giraffe.
Unlike Oxford Dictionaries, which chooses its words annually based on usage in news stories, Dictionary.com has chosen a very uncommon word. Indeed, the word does not even feature in learners' dictionaries such as Macmillan (which asked me if I meant 'terriers' when I searched for it) and Longman (which included perversity, degenerate and gravesite in the list of words it thought I might have meant). Dictionary.com chose the word because they felt that it reflected the spirit of 2011 -- the stock market, politicians and public opinion have all tergiversated this year. There was a close contender for the word of the year -- insidious, which was just pipped to the post.
Tergiversate is a back-formation from tergiversation (that means that tergiversation came first -- the late 16th century, whereas tergiversate is first attested a hundred years later). Tergiversation is slightly more common, and appears occasionally in erudite news articles (there are a couple of examples on Dictionary.com).