ETYM AS. aecern, from aecer field, acre; akin to Dutch aker acorn, German ecker, Icel. akarn, Dan. agern, Goth. akran fruit, akrs field; -- orig. fruit of the field. Related to Acre.
Fruit of the oak tree: a smooth thin-walled nut in a woody cup-shaped base.
Fruit of the oak tree, a nut growing in a shallow cup.