acorn, n. [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.].

The fruit of the oak, being an oval nut growing in a woody cup or cupule. [1913 Webster]
A cone-shaped piece of wood on the point of the spindle above the vane, on the mast-head. [1913 Webster]
See Acorn-shell. [1913 Webster]

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OXFORD DICTIONARY

acorn, n. the fruit of the oak, with a smooth nut in a rough cuplike base.

Idiom

acorn barnacle a multivalve marine cirriped, Balanus balanoides, living on rocks. acorn worm any marine wormlike animal of the phylum Hemichordata, having a proboscis and gill slits, and inhabiting seashores.

Etymology

OE {aelig}cern, rel. to {aelig}cer ACRE, later assoc. with OAK and CORN(1)

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