ion noun \ˈī-ən, ˈī-ˌän\
: an atom or group of atoms that carries a positive or negative electric charge as a result of having lost or gained one or more electrons—see anion, cation
: a charged subatomic particle (as a free electron)
Seen & Heard
What made you want to look up ion? Please tell us where you read or heard it (including the quote, if possible).