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:

Fever \Fe"ver\ (f[=e]"v[~e]r), n. [OE. fever, fefer, AS. fefer,
   fefor, L. febris: cf. F. fi[`e]vre. Cf. Febrile.]
   1. (Med.) A diseased state of the system, marked by increased
      heat, acceleration of the pulse, and a general derangement
      of the functions, including usually, thirst and loss of
      appetite. Many diseases, of which fever is the most
      prominent symptom, are denominated fevers; as, typhoid
      fever; yellow fever.
      [1913 Webster]

   Note: Remitting fevers subside or abate at intervals;
         intermitting fevers intermit or entirely cease at
         intervals; continued or continual fevers neither remit
         nor intermit.
         [1913 Webster]

   2. Excessive excitement of the passions in consequence of
      strong emotion; a condition of great excitement; as, this
      quarrel has set my blood in a fever.
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            An envious fever
            Of pale and bloodless emulation.      --Shak.
      [1913 Webster]

            After life's fitful fever he sleeps well. --Shak.
      [1913 Webster]

   Brain fever, Continued fever, etc. See under Brain,
      Continued, etc.

   Fever and ague, a form of fever recurring in paroxysms
      which are preceded by chills. It is of malarial origin.

   Fever blister (Med.), a blister or vesicle often found
      about the mouth in febrile states; a variety of herpes.

   Fever bush (Bot.), the wild allspice or spice bush. See
      Spicewood.

   Fever powder. Same as Jame's powder.

   Fever root (Bot.), an American herb of the genus
      Triosteum (Triosteum perfoliatum); -- called also
      feverwort and horse gentian.

   Fever sore, a carious ulcer or necrosis. --Miner.
      [1913 Webster]

WordNet (r) 3.0 (2006):

brain fever
    n 1: meningitis caused by bacteria and often fatal [syn:
         cerebrospinal meningitis, epidemic meningitis, brain
         fever, cerebrospinal fever]