For five years, Webster's New International Dictionary mistakenly included an entry for dord, a word which did not exist.
dord was truly a ghost word
no etymology or example of use
abbreviations were supposed to be collected in a separate section at the back of the dictionary. In 1931, a card had been prepared bearing the notation "D or d, cont/ density" to indicate that the next edition of the dictionary should include additional definitions for D and d as abbreviations of the word density. Somehow the card became misdirected during the editorial process and landed in the "words" pile rather than the "abbreviations" pile. The "D or d" notation ended up being set as the single word dord, a synonym for density.
The ghost word was banished from Webster's with hardly anyone's having noticed its presence, but it continued to rematerialize in the dictionaries of careless compilers for years afterwards.