1.Definition: a single whole grain of a cereal
"A kernel of corn"
2.Definition: the choicest or most essential or most vital part of some idea or experience
Related Noun(s):center, centre, core, essence, gist, heart, inwardness, marrow, meat, nub, pith, substance, sum
3.Definition: 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"