n 1  :  a system of body parts or organs that act together to perform some function <the digestive >  - see GASTROINTESTINAL TRACT LOWER RESPIRATORY TRACT UPPER RESPIRATORY TRACT   2  :  a bundle of nerve fibers having a common origin, termination, and function and esp. one within the spinal cord or brain - called also fiber tract  - see CORTICOSPINAL TRACT OLFACTORY TRACT OPTIC TRACT SPINOTHALAMIC TRACT  - compare FASCICULUSb   .
 
 
 
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