A ghost word called dord lived in Webster's New International Dictionary from 1934, defined as a synonym for density. It was born when an index card reading "D or d" was filed as a word rather than an abbreviation.

The slip survived multiple printings before anyone caught it, a reminder that appearing in a dictionary does not prove a word exists.

Source: As "Dord" Shows, Being in the Dictionary Doesn't Always Mean Something's a Word, Smithsonian Magazine