from
The Collaborative International Dictionary of English v.0.48
Costard \Cos"tard\ (k?s"t?rd), n. [Prob. fr. OF. coste rib,
side, F. c[^o]te, 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.
[1913 Webster]
Some [apples] consist more of air than water . . .;
others more of water than wind, as your costards and
pomewaters. --Muffett.
[1913 Webster]
2. The head; -- used contemptuously.
[1913 Webster]
Try whether your costard or my bat be the harder.
--Shak.
[1913 Webster]