The Collaborative International Dictionary of English v.0.48:

Brain \Brain\ (br[=a]n), n. [OE. brain, brein, AS. bragen,
   br[ae]gen; akin to LG. br[aum]gen, bregen, D. brein, and
   perh. to Gr. bre`gma, brechmo`s, the upper part of head, if
   [beta] = [phi]. [root]95.]
   [1913 Webster]
   1. (Anat.) The whitish mass of soft matter (the center of the
      nervous system, and the seat of consciousness and
      volition) which is inclosed in the cartilaginous or bony
      cranium of vertebrate animals. It is simply the anterior
      termination of the spinal cord, and is developed from
      three embryonic vesicles, whose cavities are connected
      with the central canal of the cord; the cavities of the
      vesicles become the central cavities, or ventricles, and
      the walls thicken unequally and become the three segments,
      the fore-, mid-, and hind-brain.
      [1913 Webster]

   Note: In the brain of man the cerebral lobes, or largest part
         of the forebrain, are enormously developed so as to
         overhang the cerebellum, the great lobe of the
         hindbrain, and completely cover the lobes of the
         midbrain. The surface of the cerebrum is divided into
         irregular ridges, or convolutions, separated by grooves
         (the so-called fissures and sulci), and the two
         hemispheres are connected at the bottom of the
         longitudinal fissure by a great transverse band of
         nervous matter, the corpus callosum, while the two
         halves of the cerebellum are connected on the under
         side of the brain by the bridge, or pons Varolii.
         [1913 Webster]

   2. (Zool.) The anterior or cephalic ganglion in insects and
      other invertebrates.
      [1913 Webster]

   3. The organ or seat of intellect; hence, the understanding;
      as, use your brains. " My brain is too dull." --Sir W.
      Scott.
      [1913 Webster]

   Note: In this sense, often used in the plural.
         [1913 Webster]

   4. The affections; fancy; imagination. [R.] --Shak.
      [1913 Webster]

   5. a very intelligent person. [informal]
      [PJC]

   6. the controlling electronic mechanism for a robot, guided
      missile, computer, or other device exhibiting some degree
      of self-regulation. [informal]
      [PJC]

   To have on the brain, to have constantly in one's thoughts,
      as a sort of monomania. [Low]

   no-brainer a decision requiring little or no thought; an
      obvious choice. [slang]
      [1913 Webster]

   Brain box or Brain case, the bony or cartilaginous case
      inclosing the brain.

   Brain coral, Brain stone coral (Zool.), a massive
      reef-building coral having the surface covered by ridges
      separated by furrows so as to resemble somewhat the
      surface of the brain, esp. such corals of the genera
      M[ae]andrina and Diploria.

   Brain fag (Med.), brain weariness. See Cerebropathy.

   Brain fever (Med.), fever in which the brain is specially
      affected; any acute cerebral affection attended by fever.


   Brain sand, calcareous matter found in the pineal gland.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Brain \Brain\ (br[=a]n), v. t. [imp. & p. p. Brained
   (br[=a]nd); p. pr. & vb. n. Braining.]
   [1913 Webster]
   1. To dash out the brains of; to kill by beating out the
      brains. Hence, Fig.: To destroy; to put an end to; to
      defeat.
      [1913 Webster]

            There thou mayst brain him.           --Shak.
      [1913 Webster]

            It was the swift celerity of the death . . .
            That brained my purpose.              --Shak.
      [1913 Webster]

   2. To conceive; to understand. [Obs.]
      [1913 Webster]

            'T is still a dream, or else such stuff as madmen
            Tongue, and brain not.                --Shak.
      [1913 Webster]

WordNet (r) 3.0 (2006):

brain
    n 1: that part of the central nervous system that includes all
         the higher nervous centers; enclosed within the skull;
         continuous with the spinal cord [syn: brain,
         encephalon]
    2: mental ability; "he's got plenty of brains but no common
       sense" [syn: brain, brainpower, learning ability,
       mental capacity, mentality, wit]
    3: that which is responsible for one's thoughts and feelings;
       the seat of the faculty of reason; "his mind wandered"; "I
       couldn't get his words out of my head" [syn: mind, head,
       brain, psyche, nous]
    4: someone who has exceptional intellectual ability and
       originality; "Mozart was a child genius"; "he's smart but
       he's no Einstein" [syn: genius, mastermind, brain,
       brainiac, Einstein]
    5: the brain of certain animals used as meat
    v 1: hit on the head
    2: kill by smashing someone's skull

Moby Thesaurus II by Grady Ward, 1.0:

160 Moby Thesaurus words for "brain":
   Vernunft, abdomen, acumen, afferent neuron, anus, appendix,
   autonomic nervous system, axon, bean, blind gut, blow to pieces,
   blow up, bowels, brains, bring down, burn to death, capacity,
   cecum, central nervous system, cerebral cortex, cognition, colon,
   conception, consciousness, craniosacral nervous system, cut down,
   cut to pieces, deal a deathblow, dendrite, discernment,
   discourse of reason, discursive reason, disintegrate, drop,
   duodenum, effector organ, efferent neuron, encephalon, endocardium,
   entrails, esprit, fell, foregut, frag, ganglion, genius, giblets,
   give the quietus, gizzard, gray matter, gun down, guts, head,
   headpiece, heart, hindgut, imagination, incinerate, innards,
   inner mechanism, insides, intellect, intellection, intellectual,
   intellectual faculty, intelligence, internals, internuncial neuron,
   intestine, inwards, jejunum, jugulate, kidney, kishkes, knowledge,
   lapidate, large intestine, lay low, leader, liver,
   liver and lights, lung, mastermind, medullary sheath, mens,
   mental capacity, mentality, midgut, mind, mother wit, nerve,
   nerve trunk, nervous system, neuron, noddle, noggin, noodle, nous,
   organ of thought, pate, perception, perceptiveness, percipience,
   perineum, peripheral nervous system, perspicacity, pistol, planner,
   plexus, poleax, power of reason, psyche, pump, pylorus, ratio,
   rationality, reason, reasoning, reasoning faculty, rectum, riddle,
   sagacity, sconce, seat of thought, sensation, sense, sensorium,
   sensory, sensory area, sensory cell, shoot, shoot down,
   shoot to death, shotgun, silence, small intestine, smarts,
   solar plexus, spinal cord, spleen, stab to death, stomach, stone,
   stone to death, strike dead, synapse, thoracolumbar nervous system,
   thought, ticker, tripes, understanding, vaporize,
   vermiform appendix, viscera, vitals, white matter, wisdom,
   wise man, wit, works



V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016):

BRAIN
       Berlin Research Area Information Network (network)


V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016):

BRAIN
       Brain Research through Advancing Innovative Neurotechnologies
(USA)


V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016):

BRAIN
       Broadband Radio Access for IP-based Networks


The Devil's Dictionary (1881-1906):

BRAIN, n. An apparatus with which we think what we think.  That which
distinguishes the man who is content to _be_ something from the man
who wishes to _do_ something.  A man of great wealth, or one who has
been pitchforked into high station, has commonly such a headful of
brain that his neighbors cannot keep their hats on.  In our
civilization, and under our republican form of government, brain is so
highly honored that it is rewarded by exemption from the cares of
office.