When:
Lookups spiked on August 23, 2011.
Why:
After a 5.8-magnitude earthquake rattled the East Coast of the U.S., many news accounts used temblor as a synonym for earthquake.
It's an unfamiliar word, more often used in journalistic writing than in everyday English.
Because of the similarity to tremor, the missing "r" is sometimes mistaken for a typo - and the word does indeed come from the Spanish for "trembling."
Photo credit: Bethany King / flickr
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Merriam-Webster unabridged