A conductor of electricity.
[Greek hodos, way.]
The ending was invented by William Whewell in 1834 when advising Michael Faraday on names for the conductors by which electricity enters or leaves a medium (originally a solution). He proposed cathode (Greek kata-, down) for the negatively charged pole by which electrons enter the medium, and anode (Greek ana, up) for the other. Faraday invented electrode from electric as a general term for either conductor. A set created later on their model describes thermionic valves with a given number of electrodes: diode, triode, tetrode, pentode; the first two now more usually refer to types of semiconductor device.