Synonyms for Nub (same or very similar meaning)
WordNet sense 1 (a small lump or protuberance):
nubble
WordNet sense 2 (a small piece):
stub
WordNet sense 3 (the choicest or most essential or most vital part of some idea or experience):
center, core, essence, gist, heart, kernel, marrow, meat, nitty-gritty, pith, substance, sum, inwardness, heart and soul
From the ODE community, based on WordNet
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