brain

In animals, the brain or encephalon (Greek for "in the skull"), is the control center of the central nervous system, responsible for behavior. The brain is located in the head, protected by the skull and close to the primary sensory apparatus of vision, hearing, equilibrioception (balance), sense of taste, and olfaction. While all vertebrates have a brain, most invertebrates have either a centralized brain or collections of individual ganglia. Primitive animals such as sponges do not have a brain at all. Brains can be extremely complex. For example, the human brain contains more than 100 billion neurons, each linked to as many as 10,000 other neurons.
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n. brain, main organ of the central nervous system, intellect, mind

(v. t.)
To dash out the brains of; to kill by beating out the brains. Hence, Fig.: To destroy; to put an end to; to defeat.
  

(v. t.)
To conceive; to understand.
  

(n.)
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.
  

(n.)
The organ or seat of intellect; hence, the understanding.
  

(n.)
The anterior or cephalic ganglion in insects and other invertebrates.
  

(n.)
The affections; fancy; imagination.
  

The brain is that portion of the central nervous system that is located within the skull. It functions as a primary receiver, organizer and distributor of information for the body. It has two (right and left) halves called "hemispheres."