Webster’s Revised Unabridged Dictionary · 1913
Costard
Cos′tard (k?s′t?rd), n. [Prob. fr. OF. coste rib, side, F. côte, and meaning orig., a ribbed apple, from the ribs or angles on its sides. See Coast.] 1. An apple, large and round like the head.
Some [apples] consist more of air than water . . . ; others more of water than wind, as your costards and pomewaters. Muffett.
2. The head; — used contemptuously.
Try whether your costard or my bat be the harder. Shak.