- The electrode which is the source of electrons in an electron tube. These electrons travel towards the anode. Its symbol is K.
- The negative electrode in an electrolytic cell. When a current is passed through the cell, positive ions travel towards it
- The electrode where reduction occurs in an electrochemical cell.
Origin & History of “cathode”
The term cathode, meaning ‘negative electrode’, appears to have been introduced by the English philosopher William Whewell around 1834. It was based on Greek káthodos ‘way down’, a compound formed from katá- ‘down’ and hodós ‘way’ (also represented in exodus ‘way out’ and odometer ‘instrument for measuring distance travelled’, and possibly related to Latin cēdere, source of English cede and a host of derived words). It specifically contrasts with anode, which means literally ‘way up’.