Dord

Dord is a ghost word, a word that never used, but accidentally added to a dictionary. In 1934, the New International Merriam-Webster Dictionary printed the word, "dord", defining it as 'density'. Philip Babcock Gove was an editor at Merriam-Webster and became editor-in-chief of Webster's Third New International Dictionary. Gove wrote a letter to the journal American Speech fifteen years after the error was caught. He explained why "dord" was printed in the second edition of the New International Dictionary. It got through when a slip was sent saying "D or d". Because the letters were typed with spaces between, it looked like it said "dord".
In 1939, five years after the dictionary was published, an editor found out that "dord" was not a word. The word was not fully removed from the dictionary until 1947. Dord is the only known ghost word in the Merriam-Webster's Dictionary's history.