Lookups spiked on April 15, 2013.
Used in some of the media coverage of the Boston Marathon bombings, surreal means "marked by the intense irrational reality of a dream."
The same word was frequently looked up after the 9/11 attacks.
A relatively new word in English, surreal dates only to the 1930s. It comes from the name of the artistic movement known as surrealism, whose effect was often created "by means of unnatural or irrational juxtapositions and combinations."