Definition
An electric current that flows in only one direction through a circuit. The magnitude of the current may vary over time, but the direction of flow does not reverse. Direct current (DC) is the most common form of unidirectional current, and pulsating DC — current that rises and falls but never reverses — is also unidirectional.
Plain English
Electricity that always moves the same way through a wire, even if it speeds up and slows down. It never flows backward.
Context Anchor
Seen in aircraft electrical system discussions, especially battery-powered DC circuits and equipment that must be connected with the correct positive and negative sides.
Derivation
From Latin 'unus' meaning 'one' and 'directio' meaning 'a directing or pointing.' Literally 'one-direction current' — the name describes exactly what it does.
Why Pilots Care
Aircraft DC systems depend on unidirectional current to deliver stable power to instruments, lights, and avionics without the reversals that would damage components.
Analogy
Think of water in a hose flowing only toward the nozzle. The flow can get stronger or weaker, but it does not reverse direction.
Intuition Check
Do not read “current” here as “present time” or moving air or water. In this term, current means the flow of electricity, and unidirectional means that electrical flow goes one way only.
Example Sentence 1
The aircraft battery supplies a unidirectional current to the starter motor and avionics bus.
Example Sentence 2
A failed diode allowed bidirectional leakage instead of maintaining unidirectional current through the circuit.