acorn /ˈeˌkɔrn, kɚ/
  橡實,橡子
  acorn
  橡實管
  A·corn n.
  1. The fruit of the oak, being an oval nut growing in a woody cup or cupule.
  2. Naut. A cone-shaped piece of wood on the point of the spindle above the vane, on the mast-head.
  3. Zool. See Acorn-shell.
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  acorn
       n : fruit of the oak tree: a smooth thin-walled nut in a woody
           cup-shaped base