early 13c., "to shy, start," perhaps from shunen "to shun" (see shun), and altered by influence of shot or shut. Meaning "to turn aside" is from late 14c.; that of "move out of the way" is from 1706. Adopted by railways from 1842. Related: Shunted; shunting.
1838, in railway use, from shunt (v.). By technicians in the sense of "electrical conductor" from 1863. Medical use dates from 1923.