Dord is one of the most famous errors in lexicography, a word accidentally created by the G. and C. Merriam Company's staff and included in the second edition of its New International Dictionary, in which the term is defined as "density".
Philip Babcock Gove, an editor at Merriam-Webster who became editor-in-chief of Webster's Third New International Dictionary, wrote a letter to the journal American Speech, fifteen years after the error was caught, in which he explained why "dord" was included in that dictionary.
On July 31, 1931, Austin M. Patterson, Webster's chemistry editor, sent in a slip reading "D or d, cont./density." This was intended to add "density" to the existing list of words that the letter "D" can abbreviate. The slip somehow went astray, and the phrase "D or d" was misinterpreted as a single, run-together word: dord. (This was a plausible mistake because headwords on slips were typed with spaces between the letters, making "D or d" look very much like "D o r d".) A new slip was prepared for the printer and a part of speech assigned along with a pronunciation. The word got past proofreaders and appeared on page 771 of the dictionary around 1934.
On February 28, 1939, an editor noticed "dord" lacked an etymology and investigated. Soon an order was sent to the printer marked "plate change/imperative/urgent". The word "dord" was excised and the definition of the adjacent entry "Dore furnace" was expanded from "A furnace for refining dore bullion" to "a furnace in which dore bullion is refined" to close up the space. Gove wrote that this was "probably too bad, for why shouldn't dord mean 'density'?"