Definition
The negative electrode of an electrochemical cell during discharge. It is the terminal from which conventional current flows out of the cell into the external circuit, and the point at which positive ions inside the cell are reduced (gain electrons).
Plain English
In a battery that is delivering power, the cathode is the negative terminal. It is the side where current leaves the battery to go do work in whatever the battery is connected to.
Context Anchor
Seen in aircraft electrical-system study, especially when learning how batteries produce, store, and deliver electrical power.
Derivation
From the Greek 'kathodos,' meaning 'a way down' (kata = down, hodos = way). Coined in the 1830s for the electrode where current was thought to descend into the cell. Knowing it means 'the way down' helps remember it as the exit/return path of the current.
Why Pilots Care
Identifying the correct terminal matters when servicing aircraft batteries, connecting a ground power unit, or jump-starting. Reversing polarity can damage avionics and electrical components in seconds.
Intuition Check
Do not assume cathode always means negative. In a battery that is supplying power, the cathode is the positive electrode; the key idea is that reduction happens there.
Example Sentence 1
When connecting the battery, the technician confirmed the cable from the negative terminal led to the cathode of the cell.
Example Sentence 2
Technicians inspect the cathode connections inside the battery to confirm no corrosion is limiting current flow.