nub
/nʌb/noun
1
the nub
the crux or central point of a matter（事情的）症结, 核心：the nub of the problem lies elsewhere.
问题的症结在其他地方。
2
- a small lump or protuberance结块, 肿块; 突起：
he pressed down on the two nubs on top of the phone.
他按下电话机上端的两个突起。
2.1
- a small chunk or nugget of metal or rock小块（金属、石头）：
a nub of gold.
一小块黄金。
词源
late 17th cent.: apparently a variant of dialect knub 'protuberance'， from Middle Low German knubbe, knobbe 'knob'.