Definition
A negatively charged ion. An atom or group of atoms that has gained one or more electrons, giving it a net negative electrical charge. In an electrolytic cell or battery, anions move toward the positive electrode (the anode).
Plain English
An atom that has picked up extra electrons and now carries a negative charge. Because it is negative, it is attracted toward the positive side of a battery or circuit.
Context Anchor
Seen in aircraft maintenance discussions about batteries, corrosion, and chemical reactions.
Derivation
From the Greek 'ana-' meaning 'up' and 'ion' meaning 'going.' Coined by physicist Michael Faraday in the 1830s to describe ions that travel 'up' toward the anode (the positive electrode) during electrolysis. Knowing this helps pair the word with its partner term, cation, which travels the other way.
Why Pilots Care
Anions are part of the chemistry behind aircraft batteries and corrosion. Understanding the basic ion picture makes battery servicing, electrolyte handling, and corrosion control easier to follow.
Intuition Check
An anion is negative, not positive. The 'an-' at the start can mislead — remember it goes to the anode (positive terminal) precisely because the anion itself is negative and is pulled toward the opposite charge.
Example Sentence 1
Inside the battery, anions migrate toward the positive plate while cations move the other way.
Example Sentence 2
Mechanics observe anion behavior when servicing lead-acid batteries installed in light aircraft.