Merriam-Webster's Collegiate® Dictionary, 11th Edition
BEAN
I. noun
Etymology: Middle English bene, from Old English bēan; akin to Old High German bōna bean Date: before 12th century
1. broad bean , the seed of any of various erect or climbing plants (as of the genera Phaseolus and Vigna ) of the legume family other than the broad bean, a plant bearing beans, an immature bean pod used as a vegetable,
2. a valueless item, the least amount , any of various seeds or fruits that resemble beans or bean pods ,
4. exuberance , nonsense , bunkum , head , brain , a protuberance on the upper mandible of waterfowl,
II. transitive verb
Date: 1910
to strike (a person) on the head with an object