Definition of costard in US English:

costard

(also Costard)

noun

British
  • 1A cooking apple of a large ribbed variety.

    • ‘The cooking equivalent was the Costard, which gave rise to the term costermonger, first applied to apple salesmen.’
    1. 1.1humorous, archaic A person's head.
      skull, cranium, crown
      View synonyms

Origin

Middle English: from Anglo-Norman French, from coste ‘rib’, from Latin costa.

Pronunciation

costard

/ˈkästərd/