kernel
noun.
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
Synonym: meat
noun.
a single whole grain of a cereal
a kernel of corn
noun.
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|the nub of the story
Synonym: center, sum, substance, pith, nub, nitty-gritty, meat, marrow, inwardness, heart and soul, heart, gist, essence, core, centre