1. [n]  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"
2. [n]  a single whole grain of a cereal; "a kernel of corn"
3. [n]  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"

1. \Ker"nel\, n. [OE. kernel, kirnel, curnel, AS. cyrnel,
   fr. corn grain. See {Corn}, and cf. {Kern} to harden.]
   1. The essential part of a seed; all that is within the seed
      walls; the edible substance contained in the shell of a
      nut; hence, anything included in a shell, husk, or
      integument; as, the kernel of a nut. See Illust. of
      {Endocarp}.
            ' A were as good crack a fusty nut with no kernel
                                                  --Shak.
   2. A single seed or grain; as, a kernel of corn.
   3. A small mass around which other matter is concreted; a
      nucleus; a concretion or hard lump in the flesh.
   4. The central, substantial or essential part of anything;
      the gist; the core; as, the kernel of an argument.
   

2. \Ker"nel\, v. i. [imp. & p. p. {Kerneled}or {Kernelled};
   p. pr. & vb. n. {Kerneling} or {Kernelling}.]
   To harden or ripen into kernels; to produce kernels.
   

(Note: NOT "kernal").

1. The essential part of Unix or other operating systems, responsible for resource allocation, low-level hardware interfaces, security etc. See also microkernel.

2. An essential subset of a programming language, in terms of which other constructs are (or could be) defined. Also known as a core language.