noun the inner and usually edible part of a seed or grain or nut or fruit stone.
— synonyms: meat
noun a single whole grain of a cereal.
noun the choicest or most essential or most vital part of some idea or experience.
— synonyms: substance, core, center, centre, essence, gist, heart, heart_and_soul
Examples
“the kernel of an argument”
“The Linux kernel is open-source.”
“The Dirichlet kernel convolved with a function yields its Fourier series approximation.”