What does acorn mean?
The definition of acorn
A”corn, n.
Etym: [AS. æcern, fr. æcer field, acre; akin to D. aker acorn, Ger. ecker, Icel. akarn, Dan. agern, Goth. akran fruit, akrs field; — orig. fruit of the field. See Acre.]

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 (Zoöl.)
See Acorn-shell.