The Oxford Thesaurus An A-Z Dictionary of Synonyms - coren.

1) centre, heart, middle, nucleus, inside(s) : Remove the core of the apple first. 2) essence, marrow, heart, pith, gist, quintessence, sum and substance: The core of the problem is her refusal to consider any alternative. --v. 3) pit, seed: The pie might have tasted better if you'd cored the apples first.