The Collaborative International Dictionary of English v.0.48:

Acorn \A"corn\, n. [AS. [ae]cern, fr. [ae]cer 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.
      [1913 Webster]

   2. (Naut.) A cone-shaped piece of wood on the point of the
      spindle above the vane, on the mast-head.
      [1913 Webster]

   3. (Zool.) See Acorn-shell.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Oak \Oak\ ([=o]k), n. [OE. oke, ok, ak, AS. [=a]c; akin to D.
   eik, G. eiche, OHG. eih, Icel. eik, Sw. ek, Dan. eeg.]
   [1913 Webster]
   1. (Bot.) Any tree or shrub of the genus Quercus. The oaks
      have alternate leaves, often variously lobed, and
      staminate flowers in catkins. The fruit is a smooth nut,
      called an acorn, which is more or less inclosed in a
      scaly involucre called the cup or cupule. There are now
      recognized about three hundred species, of which nearly
      fifty occur in the United States, the rest in Europe,
      Asia, and the other parts of North America, a very few
      barely reaching the northern parts of South America and
      Africa. Many of the oaks form forest trees of grand
      proportions and live many centuries. The wood is usually
      hard and tough, and provided with conspicuous medullary
      rays, forming the silver grain.
      [1913 Webster]

   2. The strong wood or timber of the oak.
      [1913 Webster]

   Note: Among the true oaks in America are:

   Barren oak, or

   Black-jack, Quercus nigra.

   Basket oak, Quercus Michauxii.

   Black oak, Quercus tinctoria; -- called also yellow oak
      or quercitron oak.

   Bur oak (see under Bur.), Quercus macrocarpa; -- called
      also over-cup or mossy-cup oak.

   Chestnut oak, Quercus Prinus and Quercus densiflora.

   Chinquapin oak (see under Chinquapin), Quercus
      prinoides.

   Coast live oak, Quercus agrifolia, of California; -- also
      called enceno.

   Live oak (see under Live), Quercus virens, the best of
      all for shipbuilding; also, Quercus Chrysolepis, of
      California.

   Pin oak. Same as Swamp oak.

   Post oak, Quercus obtusifolia.

   Red oak, Quercus rubra.

   Scarlet oak, Quercus coccinea.

   Scrub oak, Quercus ilicifolia, Quercus undulata, etc.


   Shingle oak, Quercus imbricaria.

   Spanish oak, Quercus falcata.

   Swamp Spanish oak, or

   Pin oak, Quercus palustris.

   Swamp white oak, Quercus bicolor.

   Water oak, Quercus aquatica.

   Water white oak, Quercus lyrata.

   Willow oak, Quercus Phellos.
      [1913 Webster] Among the true oaks in Europe are:

   Bitter oak, or

   Turkey oak, Quercus Cerris (see Cerris).

   Cork oak, Quercus Suber.

   English white oak, Quercus Robur.

   Evergreen oak,

   Holly oak, or

   Holm oak, Quercus Ilex.

   Kermes oak, Quercus coccifera.

   Nutgall oak, Quercus infectoria.
      [1913 Webster]

   Note: Among plants called oak, but not of the genus
         Quercus, are:

   African oak, a valuable timber tree (Oldfieldia
      Africana).

   Australian oak or She oak, any tree of the genus
      Casuarina (see Casuarina).

   Indian oak, the teak tree (see Teak).

   Jerusalem oak. See under Jerusalem.

   New Zealand oak, a sapindaceous tree (Alectryon
      excelsum).

   Poison oak, a shrub once not distinguished from poison ivy,
      but now restricted to Rhus toxicodendron or Rhus
      diversiloba.

   Silky oak or Silk-bark oak, an Australian tree
      (Grevillea robusta).
      [1913 Webster]

   Green oak, oak wood colored green by the growth of the
      mycelium of certain fungi.

   Oak apple, a large, smooth, round gall produced on the
      leaves of the American red oak by a gallfly (Cynips
      confluens). It is green and pulpy when young.

   Oak beauty (Zool.), a British geometrid moth (Biston
      prodromaria) whose larva feeds on the oak.

   Oak gall, a gall found on the oak. See 2d Gall.

   Oak leather (Bot.), the mycelium of a fungus which forms
      leatherlike patches in the fissures of oak wood.

   Oak pruner. (Zool.) See Pruner, the insect.

   Oak spangle, a kind of gall produced on the oak by the
      insect Diplolepis lenticularis.

   Oak wart, a wartlike gall on the twigs of an oak.

   The Oaks, one of the three great annual English horse races
      (the Derby and St. Leger being the others). It was
      instituted in 1779 by the Earl of Derby, and so called
      from his estate.

   To sport one's oak, to be "not at home to visitors,"
      signified by closing the outer (oaken) door of one's
      rooms. [Cant, Eng. Univ.]
      [1913 Webster]

WordNet (r) 3.0 (2006):

acorn
    n 1: fruit of the oak tree: a smooth thin-walled nut in a woody
         cup-shaped base

The Free On-line Dictionary of Computing (30 December 2018):

Acorn Computers Ltd.
acorn

    A UK computer manufacturer, part of the Acorn
   Computer Group plc.  Acorn was founded on 1978-12-05, on a
   kitchen table in a back room.  Their first creation was an
   electronic slot machine.  After the Acorn System 1, 2 and 3,
   Acorn launched the first commercial microcomputer - the
   ATOM in March 1980.  In April 1981, Acorn won a contract
   from the BBC to provide the PROTON.  In January 1982 Acorn
   launched the BBC Microcomputer System.  At one time, 70% of
   microcomputers bought for UK schools were BBC Micros.

   The Acorn Computer Group went public on the Unlisted
   Securities Market in September 1983.  In April 1984 Acorn won
   the Queen's Award for Technology for the BBC Micro and in
   September 1985 Olivetti took a controlling interest in
   Acorn.  The Master 128 Series computers were launched in
   January 1986 and the BBC Domesday System in November 1986.

   In 1983 Acorn began to design the Acorn RISC Machine (ARM),
   the first low-cost, high volume RISC processor chip (later
   renamed the Advanced RISC Machine).  In June 1987 they
   launched the Archimedes range - the first 32-bit RISC
   based microcomputers - which sold for under UKP 1000.  In
   February 1989 the R140 was launched.  This was the first
   Unix workstation under UKP 4000.  In May 1989 the A3000
   (the new BBC Microcomputer) was launched.

   In 1990 Acorn formed Advanced RISC Machines Ltd. (ARM) in
   partnership with Apple Computer, Inc. and VLSI to develop
   the ARM processor.  Acorn has continued to develop RISC
   based products.

   With 1992 revenues of 48.2 million pounds, Acorn Computers was
   the premier supplier of Information Technology products to
   UK education and had been the leading provider of 32-bit RISC
   based personal computers since 1987.

   Acorn finally folded in the late 1990s.  Their operating
   system, RISC OS was further developed by a consortium of
   suppliers.

   Usenet newsgroups: news:comp.sys.acorn,
   news:comp.sys.acorn.announce, news:comp.sys.acorn.tech,
   news:comp.binaries.acorn, news:comp.sources.acorn,
   news:comp.sys.acorn.advocacy, news:comp.sys.acorn.games.

   Acorn's FTP server (ftp://ftp.acorn.co.uk/).

   HENSA software archive
   (http://micros.hensa.ac.uk/micros/arch.html).  Richard
   Birkby's Acorn page (http://csv.warwick.ac.uk/~phudv/).
   RiscMan's Acorn page (http://geko.com.au/riscman/).
   Acorn On The Net (http://stir.ac.uk/~rhh01/Main.html).
   "The Jungle" by Simon Truss
   (http://csc.liv.ac.uk/users/u1smt/u1smt.html).

   [Recent history?]

   (2000-09-26)