Costard

A Concise Dictionary of Middle English from A.D. 1150 to 1580 · 1889 · p. 6

sb. a kind of apple, Prompt., ND; humorous expre ion for the head, Sh. , ND; costarde , S3; costard , a cap, ND. It probably means the ‘ribbed apple.’—OF. coste + ard , see SkD (p. 796).