kernel
noun
1 the squirrel cracks the nut's shell and extracts the rich kernel seed, grain, heart, core, stone, nut.
2 the foreword contained the kernel of the policy
ESSENCE , core, heart, essential part, essentials, quintessence, fundamentals, basics, nub, gist, substance, burden, heart of the matter, marrow, meat, pith, crux; informal nitty-gritty, nuts and bolts, brass tacks.
3 there may be a kernel of truth in what he says
NUCLEUS , centre, germ, grain, nugget.