kernel
[C/U] Both
pl: kernels
This word evokes the image of a hard outer shell protecting a valuable, concentrated center. It suggests that the most vital essence is hidden and requires effort or stripping away layers to be reached. In technical and intellectual contexts, it carries a connotation of absolute necessity. While other components may be optional or peripheral, the kernel is the indispensable engine that allows the entire structure to function.
Countable when referring to a single seed or a specific software version (a kernel of corn). Uncountable when referring to the general concept of a central essence (there is some kernel of truth here).