Semantic play time....
It seems that the definition of "kernel" in other contexts may be useful. In general, it is the one basic piece of something that you have to have--even if you have nothing else. So in a computer, it's the one thing you need first--simplistically, it manages all of the traffic between programs, devices, and user input/output.
To be more precise, the kernel + the cpu really perform the central function described above.
Note that the kernel CAN have all the hardware drivers built in, but it doesn't have to.
