means A material—silicon being the famous one—whose ability to conduct electricity sits between a true conductor and an insulator, and can be precisely controlled, making it the foundation of transistors, chips, and nearly all modern electronics.

from A modern compound, built piece by piece: 'semi-' from Latin, meaning 'half' or 'partly,' bolted onto 'conductor,' from Latin 'conducere,' 'to lead together' (con- 'together' + ducere 'to lead'). So literally a 'half-leader' of electricity. The 'conductor' of electrical science predates the electronics age, but 'semiconductor' is a child of the late 19th and 20th centuries, when physicists noticed certain substances stubbornly refused to be either good wires or good barriers—and engineers eventually learned that this very stubbornness, properly coaxed, could be made to compute.