Study the analogy Grain : Husk :: Nut : ? and choose the missing word.

The relation is the part that is eaten : the hard outer case that is thrown away. The husk is stripped off the grain before it is used; the shell is cracked off the nut. 'Kernel' and 'Seed' both name the edible inside, so they repeat the first word instead of answering it, and oil is something pressed out of the nut rather than removed to reach it.