(n): any part of a plant or fungus
(n): a single whole grain of a cereal
(n): dry seed-like fruit produced by the cereal grasses: e.g. wheat, barley, Indian corn
(n): the choicest or most essential or most vital part of some idea or experience
(n): the sum or range of what has been perceived, discovered, or learned
See hogshead.
sometimes kernel as in corn, other times kernel as in Linux.