Answer:
When I'm writing about atoms, often what I'm writing about applies to (monatomic) ions too. It's slightly annoying to add "(or ions)" after every mention of atoms, where a word that refers to both atoms and ions would be ideal. Does such a word exist?
There is "element", but often this is used to refer to multiple atoms of the same element, whereas "atom" and "ion" clearly refer to a single atom or ion.
An example: "An isotope is an atom (or ion) of the same element but with a different number of neutrons."
