Relating to or denoting the part of the autonomic nervous system consisting of nerves arising from ganglia near the middle part of the spinal cord (T1-L2), supplying the internal organs, blood vessels, and glands (raises blood pressure and heart rate, constricts blood vessels, and dilates the pupils when under stress), and balancing the action of the parasympathetic nerves.

In the 18th century, Jacob B. Winslow applied the term specifically to nerves. 

For a more extensive history, see the following resources: (1) Sympathy, Sympathetic. Evolution of a Concept and Relevance to Current Understanding of Autonomic Disorders (S57.005) Alexandru Barboi Neurology Feb 2013, 80 (7 Supplement) S57.005 (2) Olry, R. (1996). "Winslow's contribution to our understanding of the cervical portion of the sympathetic nervous system". J Hist Neurosci. 5 (2): 190–6. doi:10.1080/09647049609525666. PMID 11619046