Generations of reference books once included this term, including the first edition of the Encyclopaedia Britannica, dated 1771: “the name of an ancient cap of state worn by the kings of England, the upper part whereof was in the form of a double crown”.
The word first appeared in that spelling in Abraham Fleming’s edition of Holinshed’s Chronicles in 1587 and later included in dictionaries, including Nathan Bailey’s of 1721 and Noah Webster’s of 1828. A very few writers outside reference works have used it:
The chandelier is of abnormous size, for any number of glittering festoons have been added to its crystal abacot.
Twice Round the Clock, or The Hours of the Day and Night in London, by George Augustus Sala, 1859. Abnormous means irregular or misshapen.
James Murray, the famous editor of the Oxford English Dictionary, found that the original word was bycoket, which was indeed a form of headgear, a cap or headdress with a peak both in front and behind, whose name he thought derived from an Old French term for a small castle crowning a hill. He declared abacot to be a ghost word and wrote in an article in the Athenaeum in February 1882: “There is not, never was, such a word”. His entry for abacot in the first edition of the OED read in its entirity “a spurious word found in many dictionaries, originating in a misprint of bycoket.” In the bycoket entry, he told the story:
Through a remarkable series of blunders and ignorant reproductions of error, this word appears in modern dictionaries as abacot. In Hall’s Chronicles a bicocket appears to have been misprinted abococket, which was copied by Grafton, altered by Holinshed to abococke, and finally “improved” by Abraham Fleming to abacot (perhaps through an intermediate abacoc); hence it was again copied by Baker, inserted in his Glossarium by Spelman, and thence copied by Phillips, and so handed down through Bailey, Ash, Todd, etc., to 19th century dictionaries (some of which provide a picture of the “abacot”), and even inserted in dictionaries of English and foreign languages.
One may instead argue that since the word has — albeit rarely — been used, then it exists and ought to be treated as such. There is, after all, no shortage of words that have been grossly altered through popular error. The revision of its entry in the Oxford English Dictionary in December 2011 takes this view, giving 13 citations of its use from 1548 to 1951 and omitting Murray’s comment.
Notwithstanding that modern revisionist view, the word remains an awful warning to the writers of reference works who may be tempted to copy material from earlier works without checking their sources.