Encyclopedias have a tradition of inserting a fake entry to protect their copyright. If workers find that entry up in another source, they know they've been stolen from.
I'd never heard of this until I read a New Yorker article about a fake entry being inserted into the latest New Oxford American Dictionary. Word got out that it started with an E, so someone set to combing. The investigator got down to 360 words that weren't also in Webster's Third New International. Those were pared down to six suspects.
earth loop--n. Electrical British term for GROUND LOOP.The New Yorker mailed those words to nine experts, including Copy Editor's Wendalyn Nichols, who voted for esquivalience, and Will Shortz.
EGD--n. a technology or system that integrates a computer display with a pair of eyeglasses ... abbreviation of eyeglass display.
electrofish--v. [trans.] fish (a stretch of water) using electrocution or a weak electric field.
ELSS--abbr. extravehicular life support system.
esquivalience--n. the willful avoidance of one's official responsibilities ... late 19th cent.: perhaps from French esquiver, "dodge, slink away."
eurocreep--n. informal the gradual acceptance of the euro in European Union countries that have not yet officially adopted it as their national currency.
With guess in hand, a call was made to America's Lexicographical Sweetheart -- and she spilled the beans.