Dord

Dord is a truly great ghost word if there ever was one. The original Webster's New International Dictionary listing was like this: D or d. This was an abbreviation for "density in physics or chemistry." Then, it seems that in 1931, a chemistry editor sent in a slip that read D or d, cont./density. The point was to add density to the list of words that the letter D can abbreviate.

And, it seems these slips used hyphens to separate letters. So, it read D-or-d. Whoever was inputting this entry viewed it as a word (dord) rather than seeing it as a choice, D or d. It made it into the dictionary in 1934 and the error was discovered five years later ... yet it continues to appear.