kernel in WordNet English dictionary

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"; "the nub of the story"
   kernel  substance  core  center  centre  essence  gist  heart  heart and soul  inwardness  marrow  meat  nub  pith  sum  nitty-gritty 
   
2. a single whole grain of a cereal
   "a kernel of corn"
   kernel 
   
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"
   kernel  meat