Dictionary.net

A spurious word, given in all dictionaries, and said to mean "a cap of State, wrought up into the shape of two crowns, worn, formerly by English kings." But both word and thing are delusions. The true word, Bycocket [O.Fr.], not uncommon up to and after 1500, after undergoing a series of corruptions, appears in Spelman's Glossarium (1664) as "Abacot," with the above explanation ; whence it has been copied from one dictionary into another ever since. Its primitive meaning probably survives in the Sp. bicoquin, a cap with two points. As Henry V. on his bassinet at Agincourt, and as Richard on his helmet at Bosworth, wore a gold crown ; so Henry VI. (crowned King of England and of France) wore at Hedgley Moor two crowns upon his bycocket-but in no sense as part of it. (See Dr. Murray's Letter to the Athenaeum, February 4, 1882.)