Ion
Etymology
From Greek "ion" (going), the present participle of "ienai" (to go), because ions migrate toward electrodes. Michael Faraday introduced the term in 1834 on a suggestion from the polymath William Whewell.
noun · /EYE-on/
An atom or molecule that has gained or lost electrons, leaving it electrically charged.
What it names
The charged form of matter that carries electric current through fluids and drives the chemistry of batteries, nerves, and salt water.
Example
The signals firing along your nerves are waves of sodium and potassium ions rushing across cell membranes.
Related idea
An atom is electrically neutral, its charges balanced; an ion is the same atom after it gains or loses electrons, tipping it positive or negative. That imbalance is what makes ions chemically active.