kernel

noun

1. 1

   the choicest or most essential or most vital part of some idea or experience

   the gist of the prosecutor's argument

   the heart and soul of the Republican Party

2. 2

   a single whole grain of a cereal

   a kernel of corn

3. 3

   the inner and usually edible part of a seed or grain or nut or fruit stone

   black walnut kernels are difficult to get out of the shell